My forearm hurts real bad. With my palm up it is the inside of the forearm near the elbow. Before my tendons on my arm hurt on top but now that is gone and this has appeared. Ity feels better after I warm up but still hurts. What could cause this and what is the best way to get rid of it? I play 4.5 tennis and have played with no issue for the last 20 years. Thanks!!!