[Ciera's mom]

I just got Ciera Tuesday evening, we have been home with her since Wednesday night. I took her to the vet for her check on Thursday and they said she looked really good. She is 9wks old and weighs 1.6lbs. The breeder said she gave her Science Diet small puppy bites so that is what I am giving her. Late Thursday night she started acting really strange. She pooped and then after she did she ran like her little butt was hurting her and started scooting on the rug. Then she ate a little of her food and started shaking her head and making a weird little noise and acting like she was going to throw it up, but never did. When she would lay down, she acted fine, but when she would walk she would act like her little butt was hurting again. I called the vet and they said bring her in the next morning unless she did throw up or started passing blood. When I took her in the next morning, she was not acting like that anymore and they checked a stool sample for worms and it was neg. Since then, she has acted like that a couple more times, any sugg on what could be causing this??