About 2 To 3 Days Ago I Noticed A Pimple

About 2 to 3 days ago I noticed a pimple on my almost 3 year old sons upper right thigh. I was changing his diaper later in the day and my fingernail scraped the head off of the pimple. The next day I noticed that it looked infected, I applied a warm compress to it and it broke open on its own. The following day it again had a layer of skin over it but it was bright red and on the hard side. I again applied a warm compress and it broke open and this time released blood. I am very afraid that my child has some kind of blister/ boil/pimple thing that I had myself last year. The thing is when I kept "bleeding" this on my self it eventually pushed out this weird green pocket of semi hard puss. It hurt like the dickens and I don't want to put my child thru that kind of pain. What do I do?