As a bowler who has done the same thing, and fought tendonitis for the last 8 years -
a. If you can, drop a pound in weight.
b. Get some sort of brace - not the "dial a hook" variety - just something that will support the BACK of your wrist. Master has a good one.
c. Do some exercises to help strengthen your wrist. a 1-2 pound weight, or even a soup can, can do wonders.