@mulky Think of yourself as a dangerous, cold hearted predator that takes pleasure in devouring your prey. The parasitic entities are the prey. 
First, call on your guardian angel to guard over you. Picture it as a dangerous looking, intimidating being that is just itching to rip apart any entity that tries to do you any harm. Thank it for guarding you and know you are watched over.
John Kreiter has a book on psychic vampire defense that would probably be good for you. In that book, it teaches a technique where if you see an entity like that, you take on a stance of a dangerous predator that takes pleasure in eating those entities that would mean you harm. This would be something like standing up straight, shoulders back, your feet slightly apart, your jaw set and a steely, cold look in your eyes that says "I DARE you to fuck with me because I will teach you a lesson you will never forget". Visualize a tentacle stretching out from your non-dominant hand (receiving hand) and attaching to the entity. When it attaches, see the entity get filled with fear and alarm and try to get away. You dont let it get away and you hold on to it. As you inhale, visualize yourself pulling all the life force out of this entity in an act of feeding. As you do this, the entity starts screaming in pain while you see it start withering away as the energy is drained out of it. After this, see yourself standing over it with a cold smirk on your face feeling satisfied with yourself. Allow yourself to feel all these feelings vividly. Allow yourself to fully feel feelings that you would normally never allow yourself to feel because they almost feel dangerous and dark. Realize that YOU are the predator now. Embrace those feelings. Feel the life force surging through your body that you have forcefully taken for yourself.
Learning how to balance love and light with this "powerful and dangerous" aspect within yourself is an important part of the path. If you feel resistance to this thinking that it is dark, think carefully as to why and assume that everything you have believed up to this point might be false. If you are going to be powerful, that also means you can be dangerous to those that mean you harm and you are going to have to learn to embrace that.
Those entities definitely do not like that if done with power. They wont want anything to do with you after a few times of that. There are much easier and less painful lunches for them out there and they will find that their old methods no longer work with you. Think about how this approach and those feelings are different than how the old you would handle it.
Regarding people that try to take your energy, maybe you need less friends and/or new friends. Politely but firmly communicate your boundaries and if people wont respect that, actively avoid them. If you find yourself getting lonely, build a relationship with your guardian angel/spirit guide (that works surprisingly well for loneliness). Spend time with people that want to learn and grow also. Find some people that have the same weaknesses that you had, that also want to grow and change, and gently show them how you found strength according to their ability and desire to learn. Mentoring others is the best way to learn.

In my opinion, we are incarnated for specific reasons and things we must learn. One of those things is to find a balance between love and strength. Ive noticed that many people that naturally have a lot of love are many times internally weak and need strength. Many people that have a lot of strength many times need to build their love.
Ive seem to get a lot of questions from people after I post something about the occult. Usually it involves spirits harassing them or they just feel beaten down. Knowing how to build one's inner strength is important, which can help with both these issues. Some people wait for the universe to grant them strength just because they are loving but it doesnt work that way. We are responsible for creating ourselves according to our will. Only we can do it. We alone are our own creators.
This might be a long post but if you want to build inner strength and your intention is pure, these techniques can radically change your life. I will underline points to pay particular attention to.
In all energy work, the keys used are visualization, breathwork, emotion and intention. Ritual is used as a way of intensifying emotion and intention.
This requires you to have a healthy relationship with strength and power. If you reject strength and power, it will always be a problem. This is similar to people thinking rich and prosperous people are evil and selfish. They attract poverty and weakness like a powerful magnet and repulse prosperity.
1. Get yourself comfortable in your sacred space. Breathe deeply through the diaphragm and scan your body to release any muscles that are not relaxed. Lock onto the present moment as it flows and stay there.
2. First thing is to concentrate the mind. Many "energy workers" have very little energy because they dont know whats important in building energy. This can be done by simply staring intensely at a point, such as a candle or dot. Focus harder than you have ever focused in your life. After about 10-15 minutes, you should feel an obvious shift in your consciousness. After you feel the shift, you are ready to work with energy. Skilled meditators can get into this spot like flipping a switch. When you are in this spot, lock yourself into it.
3. Next, I like to clear the area and myself of any negative energies. There are banishing and cleansing rituals but my favorite way to do it is to chant the divine's name 3-5 times. Then I express gratitude to the divine and ask for guidance. Chanting is done similar to how the Tibetan monks do it. Its like a low, monotone vibration. After you do this, allow yourself to fully feel the divine energy in the room. 
4. Next, you will raise your vibration and purify yourself by utilizing gratitude. Gratitude is an extremely powerful energy that can be utilized for healing and building internal strength and love. Turn your attention to some things you are grateful for in your life. It could be something as simple as being grateful for the extreme beauty you experience in nature. See, in your minds eye, a small spark in your chest. This spark represents the gratitude you have summoned. As you exhale, purify yourself by releasing attachments, fears and aversions. Feel your body relax even more as you release these.
5. FULLY FEEL THE GRATITUDE. FEEL IT. FEEL IT. FEEL IT. - with all the intensity you can muster. I put this as a separate point because it is so important.
6. Turn your attention to the divine energy you have called into the room. As you breathe in deeply, see liquid light being absorbed into your body with with your breathe. This light represents the energy of gratitude. You are drawing it in from the divine as a source outside yourself to get something you dont yet have. As you exhale, you see the displaced negative energy being expelled. As you breathe in this light, see the light in your chest getting brighter and brighter until it shines like the sun. FULLY FEEL THIS INTENSE GRATITUDE.
7. Next you are going to transmute this high vibrational energy of gratitude into high vibrational inner strength. This type of transmutation is referred to as inner alchemy in the occult. Start to feel this strength. Allow this feeling to grow in intensity. Feel this strength coursing through your body. Notice your posture. Are you sitting like a god/goddess? How does a king/queen hold their head? FULLY FEEL THIS STRENGTH.
8. Know and accept that your "identity" is simply what you are in this exact present moment and has nothing to do with the past. Know and accept that this strength is "attaching" to your energy and permanently changing you bit by bit. Be mindful of doubt as that will detract from your efforts.
You can work with this regularly and take it to whatever level you choose but its a very powerful technique. I like to end any session with gratitude and devotion towards the Divine.