What Does Dark Spots On My Chest And Back Imply?

Hi I'm a 44 year old female with a skin problem. I have a flat Brown/dark purple color spots on my chest and back. I have been to so many Dermatologist and no one seem to find the problem. before the spots apper i had a very itchy rash. please help me I try to cover it with makeup but I'm realy upset becauce in never had a problem with my skin ever. Thank you