Read Bob Rotella's book Golf is not a game of Perfect. It is a really good book and believe it or not, everyone I talk to including myself has seen lower scores using his advice.
It addresses exactly the proper way to handle the thoughts that you are trying to cope with.
It is an easy read and I read it in one evening. I got it out of the Public Library, so you don't even have to buy it if you don't want to.
ISBN 0-684-80364-X
Chessbum...