What you probably had was a tear in the region of the belly button which has subsequently got infected because it has a high concentration of bacteria within it. It is best to dress the belly button on a regular basis with some antibiotic ointment after washing the area with soap and water. This would heal eventually. In addition, get an abdominal surface ultrasound
done because that would reveal the presence of any hernia
in the abdominal wall and also in the region of the belly button.