I Have A Rash Which Started About 24 Hours Ago.

I have a rash which started about 24 hours ago. It originally started on my stomach around the belt line. It is now still there but has spread to my thighs inside and out. Also my wrists and behind my ears. it is extremely itchy and burns. It started yesterday afternoon and the first sign that something was happening is my face became flushed and warm. Similar too much exposure from the sun.