What Causes Itchy Red Rashes On Body?

I have this red rash come up almost over night. I thought I had been bitten by flea's at first but the next morning, it is all over my body. Patches, round about 20-30 mm round that have joined together. some patches are 150mm long by 50mm wide. even on palms of hands and feet. Raised red, feels hot to touch. Only thing that changed in diet was cashew nuts, about 150 grams over three days. Never had a problem with peanuts before, which I eat often. The wife did change the washing liquid to earth wise, which is supposed to not have chemicals that harm you in it. That is the only changes. I did see a doctor, he said it was the washing liquid. He gave me cetirizine twice daily. Did some blood test that he said was ok, been a couple of days and it has got worst is some areas, legs, feet ankles little puffy, arms hands. But some of the torso has got a bit better. Itchy all over but worst in hands, legs below Knee's and hands. Any Ideas.