Sounds to me like you had an infection in your belly button (this could have been caused by anything) you have scratched it, maybe at first in your sleep &/or while cleaning your belly button & this has led to the infection spreading.
If this were most other places you could probably treat it with antiseptic cream or fluid & by keeping it really clean & dry. But the belly button is one of those places that we can't see, can't be sure it's dry (you do sweat there too) can't be sure no fluff is there (& if you check too often or scratch anywhere while checking you could make the infection worse & it will spread even more) so I suggest you see a dr & get the right cream - by now it & you may need anti-biotics.
Of course I could be overreacting but I can't see it & actually you can't see the centre of the problem either.