I have like a knot under the skin of my armpit lol. It's like the size of a dime and hurts, when I squeeze it, it occasionally puts out puss but not like a pimple would, you can tell it's an infection. It's not an ingrown hair, I checked about that. And it isn't an infected cut because it's more of like a cyst under the skin, I can grab the whole thing... What else could it be?