Collagenous colitis is also called microscopic colitis; it is an autoimmune disease that is only visible by examining biopsy samples under a microscope. It is more common with those of us with celiac disease. I try to manage mine with diet and de stressing. Everyone is different in what works, I eat yogurt and kombucha for probiotics, also some psyllium husk/water (soluble fiber feeds "friendly" bacteria and insoluble adds bulk, and may also bind with bile that can irritate the colon. ) As always, check with a doctor before you make a big change in diet or pills. https://my.clevelandclinic.org/health/diseases/17227-microscopic-colitis https://www.hopkinsmedicine.org/health/wellness-and-prevention/foods-for-diverticulosis-and-diverticulitis