Could be a tooth abscess...a sticker cyst...If you post apic we might be able to tell..3 months old is a bit young for CL...so that would not be my first thought....I would clean the area well and put iodine on it to help the drying and keep it disinfected..
Any picture helps - you can put a circle around the old abscess. It will help us to be able to tell you if it's something like a sticker orbug bite that you just need to make sure it's cleaned out or a tooth abscess that might come back.
not that we can tell everything from a photo but it can help.
also, if it was from something like a bee sting, splinter, sticker, something, you need to make sure that piece of debris is out of the abscess hole or the abscess will come back.