I keep getting a yeast infection over and over again. why?

I first got a yeast infection and went to the doctor and got medication for it. and me and my boyfriend had like normal. but then i got it back and after that i got it back again. is it on my boyfriends junk and i keep getting it back from him.? my doctor said it's yeast for sure. she looked at it under a microscope. the symtoms are burning and itching. and i feel bad cas it hurts all the time and i can't have with him now cas it hurts. so whats going on??? thanks