Sometimes partners can pass thrush (yeast infection) back and forth to one another. It's rare, but it happens. Your partner should be treated too. He should try using some over-the-counter yeast infection cream according to the package directions as to how often and how long to use it. Have him rub it all over his penis and especially under the foreskin (if he has one). Condoms can help prevent spreading it until you are both clear of the infection.
Is your doctor sure it's a yeast infection and not a bacterial infection?
Have you also tried wearing breathable underwear or even going without undies for a few hours a day (like when you're sleeping)? Wiping front-to-back is also important.
If this continues to happen, you may want your doctor to test you for other things. It may be that your immune system isn't fighting off infection like it should.
I hope you find relief soon. Best of luck.