I Have A Rash/pimple Like Bumps That Have Developed On

I have a rash/pimple like bumps that have developed on my lower/middle back. This is a new event and has never been an issue before. I have not changed detergents, soaps, shampoos, cosmetics, new clothes, new bedding, or anything like this. I take a shower in the morning and a bath at night before bed. I use a mild soap (white, unscented) and at a loss. Can you suggest what is going on and how to treat it? Thank you!