Yeast Infection

I don't know why this is starting to happen but right before my period comes (like a week before), I start getting a yeast infection. It's been 3 times this year. They get really bad too where I feel like crying from the pain and the itch is unbearable. The doctor only prescribes some cream I have to put up inside for 7 days and doesn't explain what's happening. I am very concerned. Does this happen to anybody else?