I am not a doctor. But I think you need a better set of exams and or tests to diagnose the cause of your pain. I also think massage sounds like it is not really helping. Can you see a sports medicine orthopedist, a neurologist or another primary care doctor than the one you get massage from?

If you take your shirt off and stand straight with arms relaxed down at your sides, can someone look at your scapula from the back and see any winging of one, or difference between left and right side at all? How about with your arms straight up? (Scapula are the sort of flat bony wings on your upper back). Are your hips or shoulders uneven when standing straight, arms down to side?

I wonder if having more conclusive tests, imaging studies, or xrays, something that "proves" the cause of your pain, would be more diagnostic and convincing for the exam disability people.

I sympathize with your frustration and anxiety. I admire your tenacity with school in spite of the pain. Try to apply that same tenacity to getting a more concrete diagnosis of your pain, which then can lead to effective treatment and resolution.