What symptoms your dog is showing.? You have to give some more details. Anyhow, your dog might be having a serious condition called canine bloat. During this condition, gases can fill in stomach after eating that put pressure on surrounding organs. This condition cal also lead to twisting of stomach. Bloat in dogs should not be ignored because affected dog can die if not treated. Dogs can show symptom like pacing or restlessness, drooling and foamy vomiting. Blood tests are used to diagnose bloat in dogs. So, take your dog to vet for accurate diagnosis and treatment.
This dog needs to be examined by a veterinarian. A swollen stomach can be the sign of serious problems. The least serious problem in puppies can be intestinal parasites. In older dogs I would be worried about gastric dilatation which can lead to bloat, fluid filling the abdomen (secondary to tumor, heart disease, or liver problems), or a mass in the abdomen. If this is an intact female dog it is possible your dog may be pregnant. Have your veterinarian examine this dog, run screening bloodwork, and take abdominal x-rays.