Over The Past 24 Hours I Have Developed A Rash

Over the past 24 hours i have developed a rash on both legs . back of the knees and multiple hard, knots on thighs . the bumps are hard and raised and extremely itchy. behind both knees there is a group of smaller , hard bumps and the skin is intense red, like a dark red line behind each knee. i have never had anything like this before.