If i have been diagnosed with diverticulitis by ct scan do i need a colonoscopy?

Possibly: It depends some on your age and past history. Diverticulitis, an infection of the colon, can sometimes show a lot of thickening on ct scan. That can be hard to tell if the infection caused the swelling, or if a tumor is causing the thickening. It is common to recommend a colonoscopy several weeks after the diverticulitis had healed, if you have not already had one.

Yes: Yes. A few weeks after the inflammation is all well. Specially if in your late 40s or older.

You need something: You likely need some sort of followup, either repeat ct or a colonoscopy. It is always possible that the inflammatory changes seen on your scan were in fact caused by a tumor and mistakenly taken for diverticulitis. In the face of such inflammation, a tumor nidus is easily missed. Some sort of followup is warranted after everything has cooled down to make sure nothing scary is was hiding there.