Shoulder still hurts

I'm 22, female, 5'7", 170lbs, Caucasian, on birth control and some antiinflammatory medicine, I don't smoke, in the Midwest.

I posted last week about a bad flu bug and my shoulder hurting, but I ended up just going to the clinic. Flu is gone, but they couldn't figure out what was up with my shoulder. (Or more so, the doctor didn't really check it out because he was in a hurry to see other patients.)

Since Thursday, the 30th, I've had a sharp pain in the top of my shoulder and near my collar bone whenever I take a slightly deeper breath than normal. It's not as unbearable as the first day, but it isn't going away. They doctor put me on antiinflammatory pills which I was told are like a really strong ibuprofen, but they don't help. I was also told not to use the arm to much and to ice it, but it doesn't hurt to move it, and I still have full range of motion.

When I lie down on my stomach with my arms under my head, I can breathe as deep as I want and not feel a thing. What could possibly be wrong?