Sharp burning sensation in upper shoulder.

For about 5 years now I've had on and off severe burning in my upper left shoulder, almost my neck. It hurts so much that it brings me to tears sometimes and it's also warm to the touch. If I press on it, it hurts even more. It usually happens when I sit on a hard surface for too long (ie a wooden chair) or stand for too long (no matter what shoes). It is so uncomfortable and unbearable. Any suggestions/input would be helpful... I saw a chiropractor, but of course that didn't help because it's not a bone, it's a muscle.

[Caryopteris]

Massage and relaxation training with biofeedback would be my suggestions.  Additionally you may have leg length discrepancy throwing your posture off, and you should have that evaluated.  It will be very important you exercise so you stop holding tension in your muscles.