most of the time, dragging of the bum on the ground is worms. some dogs just do it just because though. my dogs are dewormed on a regular basis, but tiny still drags her bottom. we took her to the vet, and everything is fine, she's just odd! i would take your dog to the vet, just to check things out!
my one dog Zee-na does it all the time. we have had her anal sacs drained and she is free of worms.she worries me though cause she is actually bald under her tail and her high upper thighs from doing it so much.needless to say she has another appt. tomorrow.
Our puppy was doing the same thing and she needed her anal glands expressed. She has had no problems since and no more butt scooting. Sometimes they also smell around that area and their poop is skinny when they need to be expressed. Take your puppy to the vet.