Both of our golden retrievers were just over 1 year when they started estrus. However she could have had it and you didn't notice. And as jaybay said a male could have already mated with her.
If she appears to be in pain you need to take her to the vet.
The only person who can help your dog is a veterinarian. If she appears to be in pain, you must, as a responsible owner, make certain she has medical care. Since she hasn't been spayed, it's possible that a male dog has already hooked up with her during her first heat. That is not a good thing. A pregnancy in that young of a dog is very hard on the poor mother. She hasn't even reached adult status yet herself.