If your dog has had insufficient exercise, it will pace about to work off its excess energy. More commonly, however, a dog will pace about if it is stressed or unhappy. Maybe you do not let it out enough. If your dog is pacing, take it out and let it run about and play. It may also pace about if it needs to pee. Some dogs will whine at the door, so either let it out or take it out. If this doesn’t work, then refer to a vet.