What Causes Recurring Mole Under The Armpit?

hello doctor. i am andres. i have 20 years old. early this year a few months ago i removed on the hospital a moll that was hurting me badly. the really old doctor told me was nothing to worry about. now its hurting me again and the moll its growing back again in a weird shape. its below my left armpit at the height of my nipple. it makes me hurt all my side and i am afraid its cancer. please awnser at me fast since in my country all the doctors does not know anything and they leave people die. the doctor that removed my moll instead of making it be analized trew it away since "was nothing"