Would A Cortisone Help In A Shoulder Injury?

Hello Last December I had a case of dermetitis on my back near my shoulder blade... I was prescibed a cream which I had to apply 3 x a day for almost 2 months... I was using my left arm, pushing my left elbow with my right hand trying to reach the dermatis .. In doing so I did not realize I was extending my arm , until I started to get some pain, and then boom!! I was in extreme pain . I tried to move my arm or try to sleep lying down, that was merely impossible.... I was sleeping in an upright position for 3 weeks on my couch... I was first given some painkillers, that did absoulutely nothing.. Thank God, when Monday came around I say my GP, and he gave me Naprosyn 500mg for 10 days... That helped a little, did some Physio, but still to this day can t rotate my shoulder or trying to place my arm behind my back, or even trying to wear my jacket is very difficult and painful... Should I get a cortesoine shot??? I still do my daily exercises... Thank you Mary