Constant yeast infections.

My sister has had back to back, what she thinks is yeast infections. I have never had one before, so I don't know what they are like. She does the suppository medicines and it goes away and then the next day it's back. She is sexually active and they don't use protection. He uses the "pull-out" method. They aren't painful and she has some discharge. She says that the most annoying thing about it is the smell. That's really all the info I have right now. I can get more if I need it, but I would like some feedback on to what you think this is. Is it yeast infections?