Dog is dragging her bottom on floor

I recently picked up a stray dog about 11 months and a black lab who was hanging around my house. She looked like she recently had puppies. In the past 5 weeks I have fattened her up, gave her two baths, gave her a check up at the vet, treated her for fleas and for hook worms. She was spayed about 9 days ago. In the last few days she started to drag her bottom across the floor again as she was doing before being treated for hook worms. The vet checked her for hook worms when he spayed her and said he didn't see any. Is it possible she didn't get rid of them or maybe is it something else? Of course I will take her back to the vet but just wanted to know if anyone had any ideas....