A. If you can gently push the lump in and it disappears, then it is an umbilical hernia (a hole where the navel is and where the peritoneum protrudes. There could be intestines in the protrusion). You will need to monitor this for pain, swelling and enlargement. Usually this is fixed while spaying the dog. A dog which has an umbilical hernia should not be used for breeding, as it is a hereditary condition. If you cannot push the mass back into the abdomen, then there is a chance that it is still a hernia, but that the opening is closing tight around the sac and could possibly trap abdominal content. This can be life threatening. The other causes would be abscess or a tumor. Best, have your vet assess it.
Your account has been reactivated.