I had quite a painful rotator cuff injury in the early summer. Couldn't even drive a car or change gear (manual over here in the UK) it was so painful. I found the best cure was complete rest for 4 days and then light stretching. actually managed to hurt is again by doing gentle arm rotations. When I got in the pool again I only did skating drills and no switches or arm stokes for a couple of sessions.
Here's a couple of pages of strengthening exercises I found and used for you to try. Can't verify the source but they worked for me.
My advice is to stop if there is the slightest twinge. A really bad rotator cuff injury can take months to repair itself and you don't want to agrovate it.