He's just scratching his ass, you COULD do it for him.......

Scooting is when animals drag their bum on the ground or floor. It is usually a behaviour associated with dogs but sometimes cats do it as well. Dogs and cats have two little glands around their anus that produce a foul smelling fluid that gets deposited on feces when the animal has a bowel movement. It’s like their calling card and is involved in marking their territory. Every dog or cat has his own smell. That’s why animals smell each other’s butts and feces. They are just reading the other animal’s calling card. Sometimes, these glands aren’t being expressed and they become very full. The animal feels discomfort because of it and they drag their bum to try to relieve the pressure and pain caused by these full anal sacs. We don’t see cats dragging their bum as often because they try to solve the problem by licking. If your cat licks his bum a lot, more than what would be needed for normal grooming purposes, he may be experiencing problems with his anal glands. Sometimes cats will lick themselves bald around their anus when they are very irritated by the problem. Dogs will lick too but scooting is a more common manifestation of the problem for them. i took my dog to the vet because she does this a lot and he told me to put a teaspoon of bran in her food, i do this everyday and she as had no problems since.

I bet your carpet smells like dog ass. I would go to another vet who can prescribe an ointment or see if his anal glands are impacted.