Maybe it is some kind of bacteria. That's why parasite cleanses with herbs and maybe a zapper are so important imo. It's not "the answer", but it's something that has to be done to make sure.
It's also possible that the yogourt helped you where your previous probiotics did not. Maybe your previous probiotics were just junk. I've read a lot of brands there is practically no active cultures in them, and when there is, most of it dies before it even reaches the intestines. Personally, the only brands of probiotics that I like are bio-K and Threelac.