About two years ago I developed tendonitis(aka tennis elbow)in not one but both arms after a minor (I thought) change in my computer set up. After some consultation with "Dr Google" I read about a physical therapy technique called the Tyler Twist, after the PT who developed it. You can read about it here:
http://www.reuters.com/article/2009/...56D7G520090714. You do it with a Flexbar made by Theraband that you can order from Amazon. As I recall, I think it was about $15. You are warned that the exercise may increase the soreness somewhat at first, but in my case, it wasn't bad. Within 3 weeks I noticed a big improvement and I'd say it was gone in a couple of months. If you google "Tyler Twist" you will find a lot of additional information, including you tube videos of how to perform the exercise. It has been written up in physical therapy journals. It worked so well for me that I wound up never going to the doctor and getting a referral for PT. I didn't totally stop doing everything that hurt, either. Although the area does need rest, I didn't find that I had to totally rest it. In my case, playing guitar didn't cause near as much pain as shooting with my DSLR,, which is a fairly heavy camera. I had a big photo trip coming up and didn't want to suffer the whole time, and by the time I took the trip, it had improved greatly. Hope this works as well for you!