aside from these psychological suggestions, which may or may not be the answers you're looking for, I would suggest looking carefully at how you use your bow. I would start simply- 1 rest the bow on the string, 2 relax the arm supporting the weight in your bow hold - this step is preparation of the sound, 3 move the bow horizontally. Start with detached strokes with a rest between each to prepare the next- the rest and preparation should take away any anxiety and tension. Then start working on the changes... up to down, down to up. the key is to keep the weight constant while you make the change (this is harder than is sounds). Do this while looking in the mirror - the really skillful bow technique I've seen is incredibly effortless looking, while being precise. Work on relaxing the arm and trying to keep the bow on the path you want (straight or otherwise)
set aside 5-10 mins. a day with this really simple practice and in time your sound and control of the bow has to improve- I can't see how it couldn't.