I have IBS with constipation. I've seen specialists and had colonoscopies. They always prescribed fiber supplements which never helped and actually seemed to make things worse. I did some research on line..reputable links like Mayo, WebMD, etc. There I read fiber supplements don't work for everyone. When I pushed the issue with my doctor they told me to start using MiraLAX. It did help but when I first started using it I got cramps before going to the bathroom. That went away after a short time. I now use ClearLAX which is Walmart's version of MiraLAX every night. I also watch what I eat. I can't digest beef well and too much doughy stuff like pizza doesn't go well for me. I can have 1 slice of pizza but if I eat 2 or 3, I feel it within an hour of eating it. I make a LOT of soups with lots of veggies and use chicken or organic chicken broth as a base. I can't eat too much at one time so I graze throughout the day. As for what I can and can't eat..it's different for everyone so you have to experiment. I have to stay away from fiber drinks like Metamucil Psyllium Fiber though. Again..everyone is different but if I use that stuff I feel just like you described. I stick to ClearLAX.