medicines are not going to help ibs. ibs is an environment problem most likely caused by pathogens. Another western medicine blunder, but of course it deals with drugs. Reminds me of the ulcer debate in which they persecuted the guy who came up with the h. pylori theory and was later vindicated.
You might want to try some intestinal formulas like Dr. Schultz or mix your own. I use psyllium with oat bran and flax seeds with NOW phytogreens. Works quite well. I also add bulk charcoal (1 tablespoon or more)> B vitamins help and you might have to adjust your dosages for you (for instance choline/inositol seems to help more as does biotin)> You could also try some probiotics if you think yeast is the problem, I like Jarrow EPS< Dr. Ohirra's formula, and have heard good things about Flora Balance by Odennell's.