I've never taken it, but my G.I.'s nurse practitioner swore by it. I think she took it for like a month before, during and after some three weeks in Mexico and said she was the only person in her group not to get diarrhea.
Probiotics can cause gas and gas cramps, but I don't think they should cause loose stools. Maybe there is just something in it that your body does not like. You can always try Digestive Advantage for IBS--which is a lot cheaper, I noticed.