I have the same problem with thrush. I used get it when I was on Tobi, which apparently isn't that common but happened every time. For me, the Nystatin doesn't work as well as the Diflucan. As far as other advice, I agree with the people that say to brush your teeth and tongue, and rinse with something like Listerine after every single treatment. I've been doing this the last 3-4 times on Tobi and haven't gotten thrush. Good luck!
PS: The dr used gentian violet on my daughter when she was a baby, and it worked for her but was a horrible mess. We also couldn't find it over-the-counter (even by asking) anywhere. Where did you buy it, just1more?