Gosh, I'm sorry your son is going through so much. As a mom myself I can completely understand how difficult it must be for you to watch him suffer.
Has your son been diagnosed with diverticulitis?
I have diverticulosis which was diagnosed through sigmoidoscopy and colonoscopy. Diverticulitis occurs when the diverticulosis pockets become infected. As for fever, I guess if infection is present, which is what classifies diverticulitis, then one would expect fever but I wouldn't say that it would happen 100% of the time. It would probably be rare to have diverticulitis without fever though.
If you suspect diverticulosis I would encourage you to have your son consult with a Gastroenterologist to rule it out. The only way to diagnose is through sigmoidoscopy, colonoscopy.
Good luck to your and your son!
-- Debbie