Why would my belly button bulge out on one side and be sore ?

Umbilical Hernia: Symptoms of an umbilical hernia include a knot or bulge near the umbilicus. The size of the bulge may increase during lifting, laughing, straining, or coughing. Usually, the bulge can be pushed back into the abdomen. Symptoms of a serious umbilical hernia may include hernia pain or swelling, abdominal pain, abdominal swelling, vomiting, constipation, or fever. See your doctor as soon as possible.