Much of the previous information/replies are right on point, however I would like to add that yeast infections that seem to reoccur can also be the result of diet. I was suffering from yeast infections every month. It seemed as soon as I cleared one up within a few weeks there was another one.
I went with a friend to a holistic health center over a year and a half ago. When I mentioned my problem with yeast infections she asked me did I eat a lot of pizza, (yes love it). Did I eat pasta again another of my favorites and last but not least I love sandwiches and bread. These foods are high in yeast. I don't drink beer but yes there is a lot of yeast in that as well.
Becasue I had a diet high in yeast I was a breeding ground for yeast in my body. YUCK! Well I took her advice and limited my intake of these foods. I did not delete them, I just monitored how much. She also suggested that I eat yogurt once a day. The best yogurt is probiotic (that is not a brand name it is a class). Kelfer is a brand that is probiotic and sold in most health food and some grocery chains.
I am happy to report I have not had a yeast infection now for over a year and a half. I hope this helps not just you but anyone else who is suffering with ongoing yeast infections. An occasional yeast infection is one thing but recurrent means there is a little something else going on.
One other thing I would like to mention. Tight jeans and underwear are also culprits in making your crotch a natural petri dish for creating more yeast infections. Use cotton underwear and avoid silk or tricote panties or thongs.