I had to try lots of different fibers, you may also as we all tolerate fibers differently. Here's my regimen: One calcium caltrate 600D pill with breakfast, one again with dinner. Then around 9 pm I take one Calcium Polycarbophil fiber pill (generic). Of course, the best thing to do is to change your diet, my diet is based on Eating for IBS. It's low fat, no dairy, no red meat, etc. etc..
.. . If I follow the diet and take my pills right, I seem to be fine. If I eat something off the diet, even with the calciums I have problems. I tried the no carb diet and it didn't work, the blood type diet won't work as many of the foods on my list are triggers for me. So, trial and error is really the only way to find your safe niche.