My Dog Has Colitis And Howls When He Poops. Will This Ever Stop?

Most colitis is mild and self-limiting.  If this has progressed for more than 2-3 days you need to have your dog examined by a veterinarian.  I am also concerned that he howls when he defecates.  Colitis usually leads to diarrhea--this is uncomfortable for dogs but most to not vocalize in agony though they may whine or whimper.
It is possible your dog is constipated, trying to pass an impacted fecal ball or rock.  These can be very painful for dogs.
Your dog should be examined by a veterinarian, have a rectal examination performed to check for rectal obstruction, and have a fecal analysis run for bacterial overgrowth and intestinal parasites.  Your veterinarian can prescribe medication management for colitis including antibiotics if appropriate and pain medication.