The poor thing is either sick or scared. I just had a silly thought. Call the vet and ask them what that might be. Vets are doctors for animals and they will help you.
Could be bad weather coming they are very sensitive to this in that manor.
She could be in pain. Check her out and see if she yelps with pain. Make sure you push on her stomach to.
It means that your dog is probably sick and in pain and that you need to take your dog to the vet to get it properly diagnosed and treated. The sooner you go, the faster your dog should recover!