What is causing my shoulder pain?

I am a 32 year old female who has had worsening pain since I started a job where I have to sit at a computer for lengthy periods of time. I have been having right shoulder pain for 10 mos. that is like a gnawing, cramping pain just below the base of my neck. I also have pressure in the inner right forearm and numbness and tingling in my right hand which seems to be most severe in the middle, index and ring fingers. I had a shot of cortisone in my cervical spine which solved the problem for about 2 months. I have had 2 physical therapists tell me that these are clic symptoms of a bulged disc but my MRI did not reflect that. I had one doctor tell me that it is Thoracic Outlet Syndrome and another said it is just muscle spasms and I need to do more of an upper body workout. Physical therapy has helped but my sessions are limited due to insurance. I used a home decompression/traction unit but it seemed to cause severe headaches at the base of my skull. What could be causing this and what can I do to get rid of the pain?