Is the swelling deep beneath the belly button, or is it a surface issue? If it's on the surface, it may be a minor skin infection. Try swabbing gently inside the belly button a few times per day with a q-tip dipped in rubbing alcohol. If it's concerning, see your doctor.
Have you had any constipation issues? Could possibly be an internal hemroid. Your bellybutton has nothing to do with the Abbi umbilical cord so you don't have to worry about that