What Causes Red Itching Blotches Around Chest, Arms And Back?

Hi,
I keep waking up with red blotches, they are itchy but not to the point that it's keeping me up at night. We have gutted our house and cleaned and cleaned incase of dust mites but it's still happening. My partner has a few but I seem to get more. It's mostly around my chest arms and back. They start to fade after a day or two but then I'll get a fresh one. They aren't defined with a pimple or prominent bite like a mosquito bite they are just slightly raised red areas.
Thanks, Laura