I recently lost 3 inches in my gut. Mucus was, and still is, interacting with the stool and "gluing it to the walls of the colen. Two weeks of Mirilax in orange juice did the trick. Now a couple of times a week for maintainance.
There is also something, common with CF, called bacterial overgrowth. This too will cause stomach extention. Is your Gastro aware of "CF Problems"?
Bill