Pimple on armpit??

Idk what the fuck is on my armpit. It is a bumb that looks like a pimple and when I squeeze it pus comes out. But when I grab it it feels like a big solid ball underneith my skin. Could this be a boil or ingrown hair? What could I be doing wrong, like shaving wise or deodorant wise? Should I leave it alone or buy cream to put on it?