Weird rash-like under arm reaction?

Hey all, over the last two weeks I've gotten to the point of "second puberty" (lots of chest pimples, more happy trail hair etc) and now my BO REALLY stinks (yay exciting) but I have a rash like reaction under both arm pits. Sometimes itchy and kinda burny/painful. At first I had thought it was my anti-persperant so I've gone without since I first noticed the rash. Can confirm it's not my anti-persperant. Has any one else experience this? And if so has it gone away? Anything to be concerned about? Been on T solidly for about two years now.