I have a lump the size of a quarter just above my right elbow. came on within three days and getting bigger. what could it be?

Epitrochlear node: You are describing an epitrochlear lymph node. This can be related to a distal infection in the forearm or the hand. If so, it may be tender. Usually the place of it is to the inside of the arm above elbow. Of course there are other possible causes of lymph nodes enlargement. If not better in a few days you may need to get it checked. A biopsy can be done if no better or worse with no good reason

Any tenderness?: It is unusual for a mass of that size to appear and then continue to enlarge. It suggests a cyst or even an infection. That's an unusual presentation for a bursitis. If it is tender, I would recommend that you get it checked. Hope that helps.