Hello, When I Raise My Arm And Put It In

Hello, when I raise my arm and put it in an "L" position, I get a pain in the muscle...it feels like it is pulling and sore. the pain started a week or two before thanksgiving.....I went to the minute clinic at CVS before Christmas....they thought it was tendinitis and gave me an anti inflammatory and said that if that didn't work to go to my PCP....the pills didn't seem to work and I have a dr. apt tomorrow. just curious as what other diagnosis this could be. I only have the pain when I put my arm in the one certain position. Could it be that there is something pinching the nerve when I raise my arm