What Causes Periodic Swelling And Pain In Right Elbow?

Hi..My mom has a problem in her right elbow. It keeps swelling periodically and causes a lot of pain to her. Recently a doctor told us that it could be the Tennis-Elbow problem. Not sure whether he is right coz previously we had consulted 4-5 doctors and no one was able to confirm about the problem. She is taking the pills everyday before meals. If she stops the pills, the swelling starts again. Please help us to figure out what is the problem.