What Causes Red, Blotchy Rashes On The Forearms And Legs?

I had cold-like symtpoms for a few days at the end of last week (headache, malaise and fatigue mostly with a little sinus stuffiness). That has basically been better since Monday. This morning, I woke up with red, blotchy flat (like a slap) rash on forearms and legs. My wrists, knees, elbows, and hips are very sore. I am a 28 y/o female with no medical problems, no medications, no recent medications, no sick contacts, no travel, no bug bites.