It's easy to develop a resistance to a single treatment, especially if it is done periodically, in too short a period, or on its own. I couldn't really say, except all living organizing wool doo their best to adapt to a situation so that they can continue their survival.
I'm glad to hear you are using selenium and iodine, that's a very good thing for the body!
And you make me smile with your reply. :)
Taking borax internally is one of the ways to address candidiasis. I have had the vaginal infections several times myself, but from what I have been able top read, the source of the infection is usually colonies in the digestive system, not the vagina, and it just shows up in the genital area because it migrates around in the body tissues. Stuff that exists in the gut is absorbed into the blood and gets the chance to imitate and live in other tissues.