I’ve had the same problem.
It MIGHT be pancreatic insufficiency - the pancreas also produces lipase and protease, digestive enzymes that (as the names indicate) fat and protein. This can actually be masked by starches in the diet, in terms of how you poop.
Which has proved to be the case for me - I’ve monkeyed around with basically every variable, and literally the only thing that makes a difference is carb intake. Hold fat and protein steady, add or subtract carbs, and it consistently affects my bowels.
I’m experimenting with a supplement that adds the relevant enzymes, but the results are mixed so far. At first it seemed effective, now not so much. I’m going to bring it up to my doctor and get tested at my next doctor’s appointment (which is six weeks or so from now).
I do find that pysllium helps, if I take enough of it. It doesn’t get me to a normal bowel movement, but it makes me go less and adds bulk, which is better than peeing out my butt.