How to keep playing with tendonitis

I developed tendonitis in my right arm in 2008 and a physical therapist cured it in 2009 by injecting my blood into the tendon. I have not played much tennis since then but I recently played twice in 2 weeks and the tendonitis has returned, but the pain is in a different location. I read that it's a condition that rarely goes away, keeps getting reaggravated, so how do tennis players deal with it? I may be able to get the blood injection again but I guess it could return if I keep playing.