Welcome to HealingWell!
I think you need a 2nd opinion. Lesions throughout your colon is not a symptom of IBS. There seems to be something else going on in there. Your temp is also not common for IBS. You seem to have some sort of inflammation which usually indicates IBD.
IBS and IBD have similar symptoms, so they are hard to differentiate at first. However, if your scope didn't come out clear (aside from the diverticuli) then your doc should do further investigation before labeling you an IBS patient. Did he takes pictures of the lesions? Maybe you could take them to a different doc. Ask questions and speak up. Don't settle for a doc who will brush you off. Especially if you feel, in your heart, that there is something else going on.