GRACIE11
..........
Yes yeast or bacteria... Either way it would cause butt scooting... And possible infection if it gets bad. I agree with @2BullyMama with the bumps, cysts and now the butt you should get to vet, he probably needs antibiotics. Allergy test would be a good idea too.
So if Gracie has yeast infection in her ears that could cause butt scooting?