Ok, so I had problems with this for years and tried EVERYTHING that's been mentioned in this thread, and more. I'm not a doctor, and I'm assuming you actually have a yeast infection when I recount my experiences/advice, so my little disclaimer is: You should definitely confirm with a doctor that this is what's going on, and approve any and all treatments.
Here's what I've tried, and how it's gone:
1) Yoghurt - It never worked for me. If you try it, it must be plain with NO SUGAR. Candida/yeast eats sugars. Some people get the yoghurt in with a turkey baster, or by freezing it into little popsicles, but I found this too painful to tolerate.
2) Acidophilus bifidius & similar supplements - It never worked for me. No one knows whether taking it internally really helps or not. If the problem is too much candida in your GI tract that is making its way to your va-jay-jay it could help, howeve. I tried taking them internally, and I also tried emptying the capsules and putting the powder directly in my va-jay-jay. Neither worked, but it could for you.
3) Garlic - It never worked for me. You take a whole clove, crush it gently, put it inside a little cheesecloth with a string tied onto it like some kind of garlic tampon, and put it up there overnight.
4) Tea tree oil anything - This not only didn't work but caused problems. Please do not follow any advice you read on the internet about this, you can give yourself a horrible burning problem this way.
5) Removing all sugars from your diet - In extreme/recurring cases you can try to starve the candida of what it eats- sugars. But this doesn't just mean white sugar, it means anything that ends in -ose, as in lactose (dairy), fructose (in fruit), etc. You can't eat anything fermented, or drink any alcohol. There is almost nothing you can eat. I tried this diet for three months, surviving mainly on plain rice, vegetables, chicken, and vitamin pills. I lost a lot of weight, but it didn't clear up the infections. For more information google "candida diet".
6) Pao d'arco - This is a type of bark that some people brew tea from for yeast infections. I tried drinking it everyday for three months while I was on my no sugars diet, and it didn't work. It also tastes like f%&#ing bark.
7) Douching with 1 c. water & 1 tsp. hydrogen peroxide - This worked sometimes. Usually douching is a terrible idea that makes yeast infections worse, but the hydrogen peroxide makes the environment hostile to the yeast, so theoretically that's why it works. I did get this advice off the internet, but was later told by a gynecologist that it was "brilliant."
8) Stop taking any kind of hormonally based birth control - I never tried this one because I've never used birth control pills or implants/shots (they make me insane-o), but since yeast infections can be caused by hormonal imbalances, this can work for some people. Some doctors will also advise the reverse of this- to begin taking hormonal birth control- in the hopes that it will regulate your hormones.
9) Diflucan (fluconazole) repeatedly - Sometimes the yeast infections keep coming back because they're never being gotten rid of in the first place. My gyno put me on constant Diflucan for something like a month, and after that I did have a long period of no infections. This is a risky strategy and should be a last resort because you can wind up breeding a Diflucan-resistant strain, and then you're really screwed, so it should also be a last resort.
10) Pee and wash after sex - Especially the peeing helps get out anything that might have gotten into your urethra and will ultimately make it's way to your va-jay-jay.
11) Treat the outside, too - Make sure you're also treating your vulva with a cream (you can get Rx strength if necessary) so that the yeast can't creep back in.
12) Make your boyfriend/girlfriend take a shower and/or brush teeth before sex - This is just to be on the super safe side that you won't be transferring anything back and forth.
13) Stop using all lubes except silicone lube. Every other kind of lube on the market has sugars (glucose, etc) in it, and when you use it you are feeding the yeast infection directly.
In conclusion, I made it through my late teens and early twenties by a combination of the long periods of taking Diflucan (often at the same time as Monistat), douching with hydrogen peroxide, and just putting up with it. Luckily, the infections simply got less and less frequent as I got older, through my 20's. Now I hardly ever have a problem, and if I do, regular old Monistat does the trick. The cause was obviously some sort of hormonal imbalance, in turned caused by unknown factors that resolved themselves. I know that doesn't sound too helpful, but it's the truth.