New yeast infection every month

How can i stop this? I get them after sex. But, I'm having only sex with a condom everytime and he never chums in the condom and the condom never broke. I had sex only with one person and he only with me. I tried taking probiotic but it didn't help.

I stopped using soap to clean my vulva, only water. I never douche, i dont smoke, i dont eat sugar,i dont wear thongs, only cotton panties, no tight jeans, shower regularly. Tested for std its negative.

What is wrong with me????

I'm sure it's yeast, I've been to the gyn countless times