Though this may seem a little far off, I believe it is worth checking out, especially if music is important to your life purpose:
Go online and find a physical therapist. From my experience, posture imbalances can lead to even headaches, and when you say that acupuncture helps I think it may be a tightness caused by muscles lower down (eg a higher left shoulder).
Yes there is only a small possibility that it may be the cause, but I suggest that you go get a check up or body assessment with a physical therapist (they're usually for free).
