When my golden retriever was still a puppy, she tended to limp a lot, but at times would run like nothing was wrong. My veterinarian assured me that nothing was wrong after checking her thoroughly. He promised she would grow out of it and he was right. It took her until she was close to a year old. It must have to do with their rapid growth, kind of like growing pains with children. Hope you will find the same to be true with your dog.