I'm not sure if you're describing one thing, or a few. Lots of people have itchy backs this time of year-dryness, cold, and so forth. As for the rashy
spotsBirthmarks - pigmented
Liver spots
Measles, koplik spots - close-up
Mongolian blue spots and red spots, those could be eczema, clogged pores, whatnot. I'd moisturize, relax (nothing serious-sounding here), and have a doc check you out.
Best.
Dr. Rockoff