What Causes Rashes On Stomach?

I have a rash on my stomach that started out a circle diameter about 3 inches. It was itchy. Went to doctor. She said it's not Lyme Disease. Not poison ivy. Diagnosed as dermatitis. It had no blistering. It looks like a sunburn. Reddish, bluish in color. Wierd thing is that it keeps grower bigger all around the perimieter. Now covers my entire front abdomen and going onto breasts. I was in the sun without protection on that area for an entire day. Does sunburn act like this? Keep spreading...even a week later? It's not peeling though