I had both tennis and golfer's elbows; the first from topspin backhands, the second from twist serves. Rest and the eventual maturity of not trying to make magazine cover-shots all the time cured both.
Based on the way I heave a tank into my truck, I'd wager on tennis elbow. Tennis elbow exhibits pain on the outside of the elbow; lateral epicondylitis. A very common overuse injury, usually from exerting a backhanded or wrist-lifting (dorsiflexion) type motion. Clinically, a positive Cozen's sign or Mill's maneuver are typical.
Quite less common is "golfer's elbow" (medial epicondylitis) which pains the inner aspect of the elbow; aggravated elbow strain typified by a baseball pitcher's throwing motion and, of course, a golfer's swing (the trailing arm gets it).
There're other possibilites such as nerve disorders, arthritis, or debris in the joint space. But all these should be sorted out in an examination.
Make an appointment and have it checked. If the pain is tennis elbow, typical initial treatment is conservative: acutely, stop what you're doing, ice, rest, maybe pop some NSAIDS, and then consider using a brace and change your mechanics/technique. If conservative measures fail, steroid injections are a possibility -- they often work but can hurt like the s.o.b. when administered. If even that fails, surgical options may be raised. Best to not let it get that far.
