What exactly happened when you took the Welchol? For me, I have to adjust the dosage depending on what I eat and how my guts are acting up; it's not a permanent "take three-a-day" sort of medicine. Did you try adjusting your dose when it stopped working?
Also, have you identified the foods you can no longer eat? Even with the Welchol, there are a few things that are pretty verboten for me. For instance, I can't have significant amounts of caffeine--I can take caffeine in chocolate and green tea, but not in regular tea, decaf coffee or regular coffee. Also, I can't tolerate fast food much at all anymore. I am usually okay to eat it every great once in a while, like when we're on vacation or otherwise travelling, but that's like once every 6 months or so. And I can't ever have anything as greasy as KFC. Fast food pizzas also don't set well with me, although I'm okay to make a Red Baron pizza at home, provided I don't eat more than half of it and that I don't eat it too many days in a row. I can tolerate ice cream pretty well, but no fruit juices at all. Whole fruit is a bit dicey, with no raw apples at all.