Suggest Treatment For Blisters And Welts On Arm

The blisters and welts are all on my left arm; they started in a cluster in the crook, and they've spread a bit south and north. Sharp pin pricks from time to time, and crawling skin, and a generalised ache all up the arm. Perhaps I'm a bit faint and perhaps my neck is a little stiff not sure if that is general fatigue