thank you for your query.
the most probable causes for your symptoms are-
1.persistance of urachus-a small cyst
or duct that extends into the abdominal wall from the belly button may be present. This is called a urachal remnant and is a left-over from fetal life. It can at times cause bleeding and may need observation or surgery
2.infection of the skin over belly button.this area is more likely to become infected because it is moist and a good environment for bacteria or fungi to grow. If there is swelling, pain, or redness
of the skin in or around the belly button its is a sign of infection.
if you experience fever
you can start on anti-biotics and topical anti-bacterial creams.
but if the swelling increases i would suggest you to kindly get it checked by a surgeon to pinpoint the cause.
wishing you good health