How To Reduce Upper Arm Muscle Pain?

Hi Doctor when I stretch my arm up and back I get an excruciating pain in the upper arm muscle Injured my shoulder several months ago was very sore to sleep on and arched but now it is not but when I stretch in the morning wow the pain, the pain gradually goes away after a few seconds . cannot throw a ball very well or do press ups as the arm hurts too much 53 years old very athletic. Surf row mountain bike arch s a little after surfing Just wounders what I could do to fix Cheers