For Approx 5 Months I Have Been Getting A 3-5cm

For approx 5 months I have been getting a 3-5cm burning area on my scalp lasting around 3 days. Since last night it's on my left middle 2 fingers and spreading up the side of my wrist to my forearm. I can't have anything touch the arm as its like fire burn. The fingers also burn. I've previous had this burn on my inner thigh again only lasting a couple of days but never this bad in my hand. Any ideas??