I Have A Knot In My Elbow At The Joint.

I have a knot in my elbow at the joint. It is a little tender but not painful. It does hurt when I move just right, or lift with it. This has been going on for a few weeks and thought it would go away. I do not remember bumping it. I am a heavy diesel mechanic and could be a result of years of "wrenching" as we say?
Thanks, Matt