Deep rectal pain and pressure in lower left abdomen where colon should be, pressure feels more noticeable when I have to use the bathroom, any ideas?

Diverticulitis . Possible diverticular disease is a condition that occurs when a person has problems from small pouches, or sacs, that have formed and pushed outward through weak spots in the colon wall. Each pouch is called a diverticulum. Multiple pouches are called diverticula. The colon is part of the large intestine. The large intestine absorbs water from stool and changes it from a liquid to a solid form.