Do not worry! This is a common occurrence in middle aged, intact female dogs. This is known as pseudopregnancy or commonly as a "false pregnancy". It is most commonly seen about two months after a bitch is in estrous. It is caused by a hormonal imbalance, particularly progesterone. Such hormonal changes lead to breast enlargement and production (lactation) of milk. Some animals will exhibit nesting behavior. A very few will actually go into labor. It is a very good idea to have your dog radiographed, or as I preferred ultrasounded, to make double sure that the dog is not pregnant! There are cases where a dog has only ONE PUPPY and does not look pregnant (weight gain). I have seen that. It means that mother nature actually took its course without the owners knowing! False pregnancy will soon pass but dogs left intact are at a higher risk of developing breast cancer. After the condition passes immediately get your pet spayed.