What Can Cause Colour Changing Spots On Face And Neck?

Hi, I'm a 15 year old girl, and recently I began to have a rash that is even with the skin, red and uneven, it has come on a couple of times after a shower and once when I have not. It turns red then purple and fades away like a bruise after a couple of days, the spot where it comes out at feels warm before the rash appears. It does not itch nor burn. It appeared on my face and neck.