Even the smallest amount of any alcohol gives me a headache that can last all night and into the next day. could i be allergic?

Probably not: An allergy is an event that in its basic definition is mediated by an allergic (IgE) antibody specifically programmed for a foreign protein. In the instance of reactions to alcohol (mainly ethanol), consumption in any amount can cause facial redness, botching of the skin and nasal congestion. Because ETOH is a vasodilator it can feel like an allergy. As with anything causing reactions...avoid it