Pain for string players almost always comes through tension, Sorcha and Katlaughing are saying the same. Try to relax your "grip" on the bow. The "hold" should be simply to direct the bow with occasional momentary presure from the first finger to provide accents. If you find yourself "Sawing" at the strings, with a firm grip, that is where your problem comes from. Yes it looks very "traditional" and "folksy" but it can lead to the problem you are having. If you cant develope the propper "hold" for yourself, have a couple of lessons, the teacher should be able to point you in the right direction fairly quickly but be aware that it may take some time to rid yourself of a well established habbit. Good luck.