Hi, Matt

Having had diverticulitis on more than one occasion I can give you an idea of what I experienced. The first time, I experienced bad gass like pains in my lower left abdomen, with fever (103) & chills. My BM's were green and pencil like and didn't relieve the pain. Eventually the pain increased to where I was doubling over. There was no evidence of blood in my stool at the time.
Other episodes I had sharp pains in the lower left abdomen....a low grade temp and some diarrhea.
The best way to be diagnosed for diverticulitis is by a CAT scan, bloodwork, & barium enema. A colonoscopy is the best way to diagnose it because they can visualize the diverticuli and how extensive they are within your colon, however, you must be pain free and without any signs of infection.
The blood in your BM's should be looked further into. It can be due to internal hemorroids or a fissure as you mentioned but also may be due to polyps or tumors in the colon as well which should be further evaluated since they could be precancerous.
I would strongly suggest you make an appointment with your doctor or even better with a gastroenterologist to look into this further with you.
Please keep us posted ~ Goody