I don’t have experience with a colectomy, but if you specifically can’t take something with fiber, then I think that only leaves stimulant laxatives (which kind of scare me because I have visceral sensitivity and easily get GI pain) and the types that draw water into your gut, hoping to stimulate a bowel movement (like Miralax).

I didn’t have luck with Miralax; it still causes me stomach pain. However I take 300 mg magnesium citrate capsules at night and that helps me. It draws water into the gut. I believe it most often comes in 150 mg capsules. I started with that and realized two capsules work best.

Of the stimulant laxatives, my GI doctor recommended Dulcolax, but I didn’t try it, so can’t say it it would have helped. Good luck. That’s a tough spot to be in.