Have Had Allergy For About 3 Months - Red Blotching

Have had allergy for about 3 months - red blotching skin, itchy, no testing has discovered cause. Started with small itchy spot on neck, then on arms, now itching is mostly arms and top of legs - worse at night, can be some day time with no itchy. Have stopped certain foods, using non chemical household products - need to eliminate cause.