Advice Please

Hi,
I've had IBS and constipation problems for the last few years. I think the IBS is mostly related to certain foods I eat and I definately know Im lactose intolerant and that greasy foods dont sit well with me. It also takes food 5 days to pass through me, which I know is not good. I know it takes 5 days because if I eat pizza, I will get gas that day but 5 days later I will have a bad time in the bathroom. I've tried to eat better, more fiber, less junk, more vegatables and more exercise which has helped me get regular, 2-3 times/day but it still takes 5 days to pass thru. I've been on colonix for one month without seeing results and I think I will return the 2 unused months and try something else. Can you guys recommend something to try to speed up the time it takes for food to pass through me?