While it may be prudent to see your doc, he is going to want to pump it up with cortisone. It is more than likely just a form issue, I know because I have the same thing. I think it's caused from the recoil of the bow after release. Try holding the bow at different levels of tightness in the hand, and make sure you are doing a push pull release, you may be holding the bow too tight and absorbing too much of the recoil from the limbs.
We are all made a little different, and the above amy or may not be your problem, but I do think it's a form issue.
Good luck, and let us know what you find out.
P.S. What Todd Cook says above, makes a lot of sense also and should be looked into.