Trying To Determine Why My Skin Is So Painful On

Trying to determine why my skin is so painful on my upper left back, worse with exercise, nothing visible on the skin and otherwise asymtomatic, i would describe the pain as burning. symptoms around 2 weeks, intermittent. I do have an impingement onthe right shoulder with possible mild tear, no mri and am doing alot of shoulder physical therapy, but the two pains feel totally different.