A couple of thoughts.IBS waxes and wanes so it can be hard to tell if something helps or hurts unless you take it for some time.Fiber may or may not help IBS. There is no evidence that is 100% good for all IBSers every single time. The evidence is that many IBSers get better on fiber supplementation and some do not. It is hard to know whether overall fiber will end up being more of a benefit or more of a problem for you as an individual. So it is hard to say whether staying the course for 2-3 weeks to see how it is over all is worth it. If the IBS has flared up for other reasons, it may not be the fiber that is the problem right now, but it could be...K.