yeast infection that just won't go away

I have been getting yeast infections consistently for five months. I've been to the doctor and they've said it's definitely yeast infection- I've had negative tests for all STI's. The doctor usually prescribes me Diflucan, because over-the-counter Monostat inserts don't work for me. I always take Diflucan for two weeks instead of one, per doctor's orders. I also eat yogurt daily, drink Kombucha, and take probiotics. My current yeast infection still isn't going away even with this treatment. Anyone know why this is/what I can do??? The doc says "I have a resistant strain of yeast" but that doesn't give me a solution. This is the WORST!