Questions about yeast infections!!! Help plz!

J

1. Why do I keep getting reoccurring yeast infections now? This just started the last few months and it seems to always be before my period.

2. Does cranberry pills help towards getting rid of infections?

3. Can you have sex while dealing with a yeast infection?

4. Does a reoccurring yeast infection mean that I have an underlying infection? Or std?