Suggest Treatment For A Red Itchy Rash On The Ear

HI i am a 20 yr old female and noticed tuesay night that i have a red bumpy and somewhat itchy rash behind both of my ears. I havent changed detergents, shampoo, or anything of that sort. yesterday i noticed that it had spread onto the back on my neck and back and today i noticed that it has spread to my chest? anything to be concerned about or should i just continue to use my cortisone10 and dismiss it as nothing?