Is it possible you were just using the wrong kind of probiotics? I remember about a couple of years ago in a health food store, the person there was telling me that some probiotics are made out of bovine products which some people can't tolerate - she gave Udo's brand as an example, and others are made out of products more similar to our natural occuring flora. Does this make sense to anyone? I was kind of confused when she told me this and I'm still not 100% clear. I know I've tried different probiotics in the past and the one I live by is Primal Defense. It contains homeostatic soil organisms so I don't believe it's made with any bovine products.
Wind, have you tried low rise pants instead of tight high waisted ones? You don't need to get the very low ones like the teens use these days, you can get a pair that sits just below the belly, yet will not show butt crack.