Do you know for sure that it is a yeast infection? Did your ob-gyn tell you that it is? If not, I would suggest talking to her about it. She would be able to confirm if that is what it is, maybe give you some meds for it, and possibly talk about why you are getting them so frequently.
There are a few things that can cause women to get repeated yeast infections, some of them are serious, some aren't.
Make sure you pee after sex. Do not douche. Also, wear cotton underwear or none at all. If you use spermicide or condoms with spermicidal lubricant, that could be part of the problem, so you could talk to your ob-gyn about your other birth control options.