I had tennis elbow off and on for ages, and a friend suggested I try "Theraband Flexbar"...and wow, it ended up working very well for me. I was skeptical at first because it looks so basic, but I noticed a pretty major difference. I read that its not supposed to work if you already have tennis elbow and you're supposed to use it to prevent it...but in my case it did work when I had it already. Now I keep one on my desk and use it 1-2 minutes a day, and haven't had tennis elbow since.

I swear I don't work for them or anything like that, just thought I'd give my personal experience for those also struggling with tennis elbow. If you google "flexbar tennis elbow" you can see it helped other people too.