Hi, I took Flagyl when I was diagnosed with C-Dif, which is something like E-Coli and it helped alot. The C-Dif had made me so sick - diarhea, throwing up, couldn't keep food down - it was just so much more than my usual IBS that I did go to the Gastroenterologist and he made me do blood work, where the C-Dif showed up. If nothing showed up in your blood work, why would your Doctor tell you to take Flagyl? It is the quintissential drug for C-Dif and other disorders like it. Anyway, it didn't bother me and I got over the C-Dif and just returned to my regular IBS issues. Don't believe your doctor when he says you are not lactose intolerant. If you read Heather's book, IBS folks can't tolerate the whey, cassein and other components in milk products not just the lactose. It is appalling how ignorant doctors are about IBS. Just be glad we have Heather and her book. Her ideas work.