Go back and make sure there's not still a retained abscess pocket. Abscesses form loculations, or little pockets of pus. If you don't break them all up, it can come back.

Also, though, a firm sensation in the area is normal for at least a few months after. As long as it's not red/tender/hot/etc. and you're not feeling sick, it might just be normal scarring of the area.

That being said, there's no way I can tell you which it is without examining it, so go see your doc.