Hmm, now that I think of it, it does remind me slightly off a bite/sting I got while cycling to work. Never saw the culprit, and at first it merely hurt like a bee-sting. But, the thing stayed around for quite a while. And started to hurt quite badly as well, for weeks, while staying visible for longer.
The afflicted area looked smaller though, only about finger-nail sized. I currently can't find a scar, but that doesn't mean anything, as my skin is generally pretty shitty.
As for topical antibiotics - I had some flying around for a while, to combat under-skin infections due to acne. Currently use some to stick up my ear, when the skin in there gets infected for no reason at all.
So yeah, a repeat bite could look like that - or maybe an isolation pocket popped in a bad way and restarted the infection.