If it doesn't go away and continues to get worse even after stretching, icing, and OTC pain meds, see a Rheumotologist. It could be Bursitis. Mine started out like yours, but with activities it became worse (without proper stretching). I have severe Bursitis in both hips and shoulders and had cortisone shots in the Bursa of each of those joints. Not fun. Now I have to do exercises everyday for the rest of my life because of it. It started last August when I installed new kitchen flooring. I used to walk a 4 mile loop up around my house a few times a week, and spent several hours a week bent over and kneeling in my flower beds. In October my husband and family cut, hauled , and stacked 3 cord of wood. January 1st I could barely walk or move my arms, I think the Drs. thought I was nuts because I was in so much pain, I don't think they believed me. Well I changed Drs. 2 times and then was sent to a Rheumotolgist, it is severe Bursitis and Tendonitis, then came the Corti shots, instant pain relief but will have to keep stretching and exercising for ever. I still can't sleep on my sides. Sometimes being idle to long in between activities will cause this. Hope it helps and sorry my story is so long.(Oh yeah if I am not completely healed in 2 more months, I will have to have the shots all over again, and damn did it hurt, they had to go deep into the bursa). Don't mean to scare you but this may be a possibility.