VERY frequent yeast?

I've written before about yeast infections, and they've continued over the last 10 months. I go to the doc about them frequently, he gives me a treatment, and it goes away. The yeast occurs so frequently that I can have it (and be treated) upwards of twice a month. I wash thoroughly, don't let sugars and such down there, and am cautious about the fabrics I wear. Why is this happening and how can I stop it??

Rouge