Suggest Treatment For A Small Bump On The Armpit

Hi. Today i woke up for school and I was getting everything ready to go and ended up taking a shower. In the shower i was using the body wash cleaning my self under my armpits and I felt this small round bump a little below my left armpit. The bump is under my skin and slides around every time I touch it or feel it around. It hurts a little bit if I put pressure. Can it be a gland of some sort or maybe a cyst ?