Armpit bump/zit/cyst?

Mary Beth
 I found this bump on my armpit while shaving tonight. When I got out of the shower, I squeezed it and pus came out along with some blood. Pus stopped coming out but it's still a rather large bump that hurts when I put pressure on it. Does anyone have an idea of what it might be?
It won't give me the option to make it TMi so TMI...