I have IBS sometimes, too. I take Imodium when it's really bad. It's like, when I go through a bout of it, it makes me nervous, which makes the IBS worse, which makes the nervousness worse, which makes... Frustrating.

I drink a lot of diet Pepsi (usually Jazz, Black Cherry and French Vanilla, but other flavors, too), and my diet is bad, so that doesn't help.