Weird rash on my back/arms/chest?

I have had it for about 3 years now, And at first I didn't really care, it seemed to stay on my back. Over the last year or so, it has moved to my shoulders, and down my biceps, and on the crease of my elbow. It takes up a large portion of my back, and a little on my sides, too. It's in a weird shape and pattern, with no real determinable shapes, but some are round dots, like circles. When i sweat, and it gets bad, It gets red, and itchy. Sometimes, it's not itchy. And sometimes, it gets dried out and almost scaly, and just looks like a peeling sunburn, it goes a white color. All I know is, my back is itchy almost all the time, and I need to figure out what this is.