The bottom of abdomen below the belly button hurts when i cough what is this?

Could be a hernia: Increasing pressure in the abdominal area can cause a defect in the abdominal wall muscular to become apparent, which is called a hernia. If there is a bulge that you feel, or mass, this may be the intestinal contents protruding through, called a 'ventral hernia.' this can be normal in babies, but should be evaluated by your doctor in an adult.