while ago I had a sharp pain in my shoulder when I would move it at certain spots then it would go away for a few months then starts again. I just got the pain again but it hasn't gone away and its been about a week. It seems to come back when I sleep on that side on a hard bed. A long time ago When it first hurt I think I may have run into a wall really hard with my shoulder or got tackled playong football, I don't really remember. What is causeing this pain?