Boric acid is a very helpful treatment for chronic and resistant yeast infections.
Taken internally, it is toxic, so I'm inclined to be really explicit - YOU DO NOT SWALLOW IT - you apply the powder to your vulva or insert it into your vagina.
Naturopaths have suggested it for years. The reason why it works is that many women who are prone to yeast infections have neutral or high vaginal pH, whereas it should be slightly acidic (around 5 on the pH scale). Yeast can't thrive in an acidic environment. Boric acid has the right pH to make your vagina mildly acidic. I think that's why drinking cranberry juice works, too.
You can apply some of the power directly - it doesn't take much. Or, you can fill a gel cap about 1/3 of the way with the powder and insert that. It only costs about $6 for a three month supply, and many pharmacies carry it. I buy caps, and fill enough for a couple of months at a time.
Initially, you may want to use it for about one to two weeks every night (while wearing a pad). Then, just use it for a few days out of the month - when you're on your period, for example.
Stop using it if it makes you more irritated. Always wash your hands really well after touching the powder - and don't let anyone have oral sex with you until you've had a chance to completely rinse it out in a bath. Don't use it on open wounds.
With all those warnings, it sounds kind of scary, but it's really harmless and totally effective when used externally - and it's effective for strains of yeast that are resistant to other treatments. Now, I just use two or three caps a month, and it keeps the yeast at bay. I wish I'd known about it 15 years ago. Could have saved me a lot of frustration, pain (and money).
Just remember that vulodynia can have a lot of other causes than yeast (for example, sometimes foods high in oxalic acid can cause vulodynia... cranberry juice could be making it worse) . Make sure you know what you're treating before you start trying various remedies.
If it still makes you nervous, read the info on these links about using boric acid to treat yeast: http://www.med.umich.edu/obgyn/vulva/yeast.htm
Hope that helps. Lena