Itchy RED Rash

I have a itchy, sensitive, and bright RED rash on the underside of my right breast. It spreads down onto my abdomen. It's roundish, and about the size of a softball. I have large breast and thought intially that it was a heat rash, but even with hydrocortisone cream application it does not seem to be improving.  It doesn't seem to be spreading.  Is this something to be concerned about?

Thank you, in advance, for your advice.

[TatiS1]

I also have a red rash under my breast. I applied several different ointments and creams, baby powder, as well as washed it with Dove's medicated soap for sensitive skin under hot water, and still the rash does not seem to improve. It still itches and burns, what else should I do?