What Causes Pain In Elbows?

I recently starting having pain in my elbows. I noticed it when I went to reach out and hand something to a co-worker. It hurt a little more when I went to pick up a cake today. Any ideas on what it could be from? I am 25, 5 feet 4 inches, and about 190lbs. I work at a desk all day in fron of the computer and don't exercise very much.