I scoured kellymom and other resources for yeast treatment. I think we had yeast since he was born (I finally started treating it at 4 months and licked it by 5) It's no fun, but here are some things that might help:
wash your nippes with a solution of vinegar after each feeding
Goldenseal tastes horrible but is a great anti-fungal. I took it in capsule form.
Garlic is also an anti-fungal.
Some people feel that lansinoh and similar nipple ointments encourage yeast growth. I used motherlove nipple ointment. It's main ingredient is olive oil which also has anti-fungal properties. I applied it with a q-tip so as not to contaminate the jar.
I stopped wearing a bra. yeast treatment guidelines say to wash your bras everyday in hot water. who has time for this? I figured I changed my shirt daily, so I just stopped wearing a bra and got rid of the middle man. (warning: this did cause my breasts to leak more)
These are all things I used to treat the thrush, but I can't see why they wouldn't hurt to prevent it as well. Good luck!
ps. My ds had to take antibiotics recently. he's never had yogurt before and I didn't want to risk it while he was on the drugs so I gave him infant probiotics. The one I have is a powder. I'd mix half a tsp with a little water and put it in a dropper and he'd drink it down (it's pretty sweet like breastmilk). probiotics are no big deal for him or me, it's just remembering to administer them!