Why Is My Left Armpit Burning Suddenly Without Any Injury Or Irritation?

hello. my left armpit suddenly felt burning . i didnt do anything to irritating it yet. no scamratchnno nothing. it feels. like how chili burn hands. feel kinda get slice with knife. my first action was put minyak angin.on it. i want to know why are this happeng onlg to my left armpit?