Systemic Itching Rash

Over the last 2-3 months symptons have progressed and worsened. Intense itch started in ears, eyes and scalp, then palms of hands with resultant excema like blistering pustules, fiery redness, peeling. Next - intense anal, perineal and groin itch radiating from deep inside site. Armpit rash, then behind neck. Yeast culture taken at vaginal site negative. Aggravated by food sensitivities, stress and heat. Usually flares at night and early a.m. Lingering rash on hands, groin, and armpits is raised, red, and scaly. Used several topical creams containing various steroids and bendadryl topical. Oral meds include high doses of benadryl and atarax(50mg.) - some relief temporarily. Suspect systemic illness. Would like to know the underlying cause, not just treat symptons. Please help.