I have a chick with similar issues. They all started out the same size, but after a week this one is still very small, the other chicks are much bigger. It's not feathering as fast as the others either. I just cleaned it's crusty butt again and put some vaseline on it. Hope it'll grow out of it... I've never lost a chick or a chicken before, always managed to fix whatever was wrong. Hope to keep my lucky streak going.