Fleetwood...doing rotator exercises are good for anyone, but whay do you think that's your problem? It seems from your disciption that your impinging at the ac joint. The structures, bursa and tendons get inflamed or even tear slightly causing great pain and reduced range of motion. You can and should ice and wrap it over the joint immediatel;y following training. Also, some anti inflammatories (advil, 3-3 times a day, I used) for a few days to a week and see if the pain decreases...then you know it's inflammation at the joint.
Anyway, the exercises are internal, external rotation with a towel folded undewr your arm and against the body...the wil assure that your abducted and then use the small rotator muscles. Then do something rehab will call empty cans...you internally rotate your hands while down at your side (like a side lateral but turn your thumbs in ward toward your body) then raise the arm up and out to the side/front and come back down...use 3 pounds for about 50 reps for each of three exercises, ext, int, and empty cans.
