I don't know what kind of alcohol reaction this is?

If i drink a lot, the next day when I wake up my whole skin is red and itchy and lasts a week. Allergy medicine doesn't help either also. It's not an allergy because it doesn't happen immediately and i don't know if it's an intolerance. I've been to doctors but they haven't been able to tell me what it is. But they recommended I take antihistamines any time i drink to prevent the reaction so what could is be?
I don't know what kind of alcohol reaction this is?
Post Opinion