Do you know if the pain originates from drawing/holding the bow, or from releasing the bow? Sometimes I get a pain in my fingers while I am drawing the bow, and it mainly serves as a reminder to me that I should relax my fingers. Any muscle tension in the fingers, other than that necessary to form the hook, will result in inaccuracies and can also hurt.
OTOH, if the shock of releasing the string is causing the pain, it might not be as easy to fix, other than exploring different options, like a thumb ring.