I had a colonoscopy and showed no IBS
IBS cannot be seen with a colonoscopy. A colonoscopy is used to make sure it's nothing more serious. When NOTHING out of the ordinary is found, then IBS is suspected.
An intestinal infection wouldn't last as long as you've been posting.
When people have problems such as you describe. The usual course of treatment is to rule out serious conditions. This is done by blood work, a stool sample that tests for blood, parasites, c.difficile, and other things. Then usually a colonoscopy is done, sometimes a barium enema. Sometimes gallbladder scans. When everything else is ruled out, then a diagnosis of IBS can be made.