My female did the same thing, along with digging as if she was going to have another pup. I was worried so called the vet and they said it was normal, that her uterus is going back in size. It depends, it lasted for her about a week.
Our 3 year old Shih tzu did the same thing after giving birth to 5 puppies. It went on for about 3 weeks. She felt like she was burning up. She is back to normal now at 6 weeks.