I Have Pain Where The Arm Meets The Shoulder, It's

I have pain where the arm meets the shoulder, it's been about a month now. It started after I was punching a heavy punching bag. I massaged it with a hand held massager and it seemed to have gotten worst. I swim every day with the pain, one shoulder hurts more than the other. Hurts more when I lift my hand over my head. e-mail YYYY@YYYY thank you