I'm in the same boat. Lifelong constipation (I'm 55) and bloating. I was diagnosed after getting yelled by the nurse for not being sufficiently empty for my colonoscopy. I drank every drop, but it had a long way to go to reach the exit LOL. My GI doc said next time we'll start a week ahead of time rather than 2 days.

Intermittent fasting has improved my bowels considerably, and I really hope, respectfully, to never be in your shoes! No fun! Hang in there:)