you must first identify the cause. not something that i can do for you over the internet. one possible culprit would be enzymatic detergents like tide or perfumed dryer-soften sheets (bounce etc. ) that cause a "contact dermatitis". of course there can be many other considerations. until you figure it out re-wash your sheets in a milder detergent and don't use a softener. take a long-acting antihistamine at bedtime.
i have a hot itchy rash that occurs at night in bed. it mostly clears up after a shower. how do i get rid of this rash?