Welcome to the boards. This is a great place for IBS info and advice. I really don't have much to add to what the others have said. I do not take a fiber supplement....I know I'm supposed to....but they don't agree with me. I usually do pretty good unless I eat a trigger food or have a lot of stress.
Just wanted to mention to stay away from sorbitol. It is a big IBS trigger and is in lots of vitamins, gum, mints, etc.