What Causes Pain In Arm And Bicep While Stretching The Hand?

My left arm started bothering me several weeks ago. Original thought was tennis elbow. I catch a lot of pitches for my 12yr son, and have repetitive motion catching and turning the glove over to retrieve ball. Throwing arm (right) is fine. However, i ve noticed that now it hurts to straighten out the arm and the bicep hurts as well. Could this still be tennis elbow? Just spread of the inflammation ?