Rash under my boob. Tmi (cleavage)

This just started a couple days ago under my boob. I dont wear actual bras just sports bras when I'm working, so that's a very sweaty area that sometimes sits on skin as I'm a size H. It burns when it gets sweaty for the first time and that's it.. it doesn't itch Any advice? ( I know it's not std related). Tia!!