Tendonitis of the shoulder

I recently reinjured my shoulder and went into a local convenient treatment center. The doctor explained that it was a case of tendonitis of the shoulder and prescribed some anti-inflamatories, muscle relaxers, and rest. My career involves repetitive motion on a regular basis, which I believe did not cause the problem in the first place. I am an avid weight lifter and I believe I originally injured it performing some exercise. The shoulder feels fine now after a month, but I am eager to get back in the gym. Are there any light exercise I can perform to strenghthen the area w/o reinjury? Any stretching exercises or the like? Thanks.