As someone who has suffered monthly from yeast infections since my very first period (over 25 years), I can hear and feel your pain. Some women, unfortunately, have yeast tied into their female hormones/cycles. I happen to be one of them. I have tried every trick in the book (except for the garlic clove one--I am definitely going to keep that one in mind! Thanks for that idea, Christina N.) and have gone through every pharma and OTC med/remedy there is. None of them worked for me.
So I had to resort to other ways to get rid of/combat/suppress the yeast.
Along with the no thong underwear and no wearing of underwear at night (I wear COTTON pj pants, just minus the underwear), wear COTTON underwear only. Any other type of material traps moisture. That also goes for really tight/skinny pants/jeans. Avoid them.
Never use soap with smells/deoderant/sprays/perfume or anything of that nature down there. I use Dr. Bronner's Castille soap when I shower, citrus (all natural, no synthetic smells or anything).
Try changing your diet and what you eat. Try to get away from/severely limit the amount you eat of anything white and refined (white flour, white sugar, anything made with these--includes all bread, donuts, crackers, etc.) and severely limit SUGAR. Yeast converts the white and refined flour as well as it uses the sugar to feed itself. I use Sweet Leaf when I want to sweeten something or honey. When I bake I use organic raw unrefined sugar. I have severely cut out/curtailed the sweets I eat. I usually have a piece or two of dark chocolate; that fixes my sweet tooth craving. For me, diet change was the BIGGEST difference I have seen in terms of severity of symptoms and how long they last and has cut down on the number I get. Jill K. has a very good post--she is spot on for what to avoid.
If you don't take a probiotic, start. The probiotic will help recolonize the gut/intestine with GOOD bacteria and start knocking out some of the bad (the yeast). Florajen3 is very good--my daughter uses that one. It can be found in the pharmacy/refrigerator section of places like Walgreens, Target, Whole Foods, etc. I personally use Primal Defense Ultimate Probiotic.
I currently take preventive measures by taking supplements that get rid of/suppress the yeast. I take Yeastguard by Solaray and Capryl by Solaray. If I take them continuously, every day, I don't get an infection. I just had my daughter start taking them (she's 13 and just starting with her periods). For her, they actually helped stop a yeast infection she had starting. Make sure you drink a lot of water/liquids. You need to flush the yeast out of your system.
Some women have had some relief from putting unsweetened yogurt "down there" at night when they go to bed. It personally never worked for me. You can also douche with yogurt and water. I had mild success using that route. If you're going to eat yogurt, make sure you're eating an unsweetened brand (you don't want the sugar, because yeast lives and thrives on sugar). You can "sweeten" it yourself with Stevia leaf or by adding a little vanilla or cutting up fruit and putting it in the yogurt.