As has been mentioned, sugar water should only be used the first day after shipping to help boost energy. Used on a daily basis or more than a day or two, will cause diarreah. It could be what's causing the pasty butt and bad smell.
However, when I've had an outbreak of Cocci it was always preceeded with carmel colored poo and an awful, very distinctive smell. Later followed by bloody poo. Adding Sulmet to their water will kill the Cocci - feeding them medicated chick starter will help prevent it. I had a batch of 60 assorted breeds, about 3 weeks old, living in a large pen during the winter when they got Cocci, it was only a few of certain breeds that died, everyone else survived. Barred Rocks, however, are pretty stout birds, I turn mine loose to freerange at a week or two old and have never lost a one - but, they are from my own flock. It's the "fancy" breeds I've had trouble with.