I deleted your other post, which appeared to be a duplicate of this one and so far had no responses.
There are many fiber supplements out there; you can pick them up in your grocery store or pharmacy. Look for one that contains psyllium and start out slow, like Keriamon mentioned. Also, you should try fortifying your diet with bran cereals or oatmeal. Both insoluble and soluble fiber are important for the digestive tract, and most people don't get enough of both kinds, so you should try to include both types in your diet.
Let us know how it goes.
Co-moderator - IBS Forum