Reddish Rashes Under The Breast, Abdomen Getting Bigger In Size. No Pain Or Itching. What Are These?

Hello. I am a sixteen year old female and I've been experiencing a red rash of some sort on my skin for the past year and a half about. It began as a small light red circle on the underside of my breast, and slowly over the past year and a half has been spreading. Now there are many smaller ones about the size of between a pencil eraser and a dime across my upper stomach, and the one on my breast has gotten much larger. There is no pain, itching, and it is not raised (you cannot feel them), but I would like to get rid of it and I was wondering if it could be a symptom to anything more serious (even though I've had basically no health issues since I've gotten them). Thank you!