My armpit is itchy please help?

My left armpit is reallly itchy!!! Its been for a couple weeks now , but at the moment is reallly badd!! Its 12:30AM & I can't sleep because its so itchy , so I have a cold glass bottle on it right now , but as soon asI take it off, it gets really itchy again and I can't goto sleep with the bottle right here!! Any suggestions ?!