What do I do to get rid of my chronic elbow pain from old sports injury?

First need dx. First you must identlify the etiology of the pain whether it be tendonitis, instability, osteoarthritis etc. Once the problem causing the pain is identified it can be corrected or improved with nsaids, ice, appropriate stretching and strengthening or in more severe instances surgical correction.
Elbow injury. Need more specifics regarding "old injury". Best course of action is to consult with an elbow specialist, have an exam and proper radiographs so that you can be given a diagnosis and treatment plan.