I have one currently, and believe me it's not fun. It started off with redness stretching down below the belly button which would be quite painful, but i thought i had irritated the hairs, so thought nothing of it. It would often come and go.
Then i started having experiencing a hardness in my belly button, it was really painful, and it started expanding. It got larger and larger and then finally burst, at first it was pus and blood but then it started producing moo.