Hello and welcome
It seems the there is pus in it that has cause due to infection. Do not pop it till you consult your doctor. I think a course of short antibiotic will resolve it and you will get rid from it. If it rupture by it own than you can squeeze it and remove all the pus present in it. But even than you need antibiotic to heel the left wound without any infection. Take analgesic
drugs to reduce pain.