I had it too. I don't know how I got it, but it was very painful. I had to go to PT to "fix" it. Both of my sisters had it too. My older sister needed surgery for it. My shoulder is starting to bother me again now. I guess I had better start exercising it or I'll be back in PT again. UGH!!
Good luck with it. I swear those Physical therapists enjoyed hurting me!! Only kidding.... but I did often tell them that they were NOT my favorite people!! (Smiling as I said it!) I did also get a cortisone shot in the shoulder. Without that shot, I would never have even been able to let the PTs work on me!!