OMG!!! Have you sued your doctors yet?!! I am so sorry about your cancer and the treatment. You mentioned your muscle changes. I have been learning how they affect our BM's. I have smooth muscle weakness, almost no intestinal muscle movement. Mine is @ least somewhat caused from my HPTH and elevated calcium levels, for 5-7 yrs. My parathyroid glands are whacko, pushing calcium into my body when I don't need it. So, I have to have 3 1/2 of my parathyroid glands removed. No doctor ever mentioned anything about this to me and I should have been monitored for this since my celiac diagnosis. I have had CIC for 17 years. Small bowel partial blockages, 3 blockages in anus that required "digital removal ", with my finger. Been on every drug. My GI was terrific for my endoscopy that shocked me with a Celiac Disease diagnosis, I was and am asymptomatic. But when his narcissistic arrogant way of treatment was not working, he literally quit taking my calls/emails. For me, I eat a very very bland diet with little solid foods, drink meal replacement shakes (my daughter has issues too, she did all the research, so I trust the shakes). I use 3-6 capfuls of miralax to keep my 💩 runny mush-diarrhea. I was using Metamucil fiber daily, but it just makes me stopped up. I use it now, only 1-3x week, with extra miralax. I understand the pressure pain, it's terrible. It ranks up there with childbirth. Mine is usually air pressure, different than gas. I run to the toilet thinking it's 💩💩‼️, but there's a horrendous explosion of air, maybe some poop specks. I have had X-rays standing and laying of my colon every few months for 10+ yrs, my colon always (except 1x) has a moderate to heavy fecal load. I hope my story might be of some help to you. For the burning part I immediately sit on a heating pad or get in a hot bath with little water. I have also gotten over my anxiety about putting LOTS of Vaseline or hemorrhoid cream , with glove on, up my bum.