Act quickly! My son had thrush for a long time before I realized what it was, and then it took a long time to get rid of. The doctor will probably give you Diflucan or some other yeast infection treatment. It works, but it takes a while. In the meantime, boil everything that has been in your baby's mouth! Do this every day until it's gone.
If you're brestfeeding, you'll probably get a topical cream to use. Use it religiously, and also eat yogurt and take acidophilus supplements (you can get them at the drugstore in the vitamin section). It's just like treating a regular yeast infection, only in a different area. Wash your bras frequently in hot water, and use disposable nursing pads that you can change 3-4 times per day.
A friend of mine also recommended a treatment of Gentian violet (?) or something like that. It stains your baby's mouth purple and also will stain you if you're nursing. But it wears off in a few days. I never tried it cause I was afraid of making a huge mess of purple, but she said it helped, in addition to the other treatments.
You can also give your baby acidophilus. If you get capsules, you can break them open, dump out the powder, and put a little in baby's mouth. I asked my doctor, and while he hadn't heard of this, he said it wouldn't hurt to try it. Just a little on your finger maybe 3 times a day.
Actually, the best thing that helped us finally get rid of it was for me to pump breastmilk and give it to him in a bottle. (When I went back to work.) If you do that temporarily, you can always go back to nursing later.
Hope this is helpful!