I am doing physical therapy for a rotator cuff strain, and the exercises she has me doing are eye opening. All of them are long-term good for tennis movement too. Unfortunately they would be very difficult to explain in words as they are small muscle group specific.... I have to concentrate on engaging specific muscles when doing an exercise, rather than letting the bigger muscles cheat and do all the work (biceps, triceps, lats, etc.).
So my suggestion is to speak with an accredited physical therapist or trainer to evaluate your current condition specific to tennis, and then demonstrate exercises to strengthen those areas.
Everyone hurts somewhere... and then the body starts to compensate to work around the pain/discomfort... but that compensation might not be best for your tennis strokes. Strengthening or repair the injury can also be painful (trust me... it is!) but it can be long term beneficial.