Allergy is, as far as I can tell, an abnormal reaction to a substance. My feeling is you have two allergies. The one that you asked about would be to a substance other than alcohol, like the sulfites or histamines already mentioned.
The other abnormal reaction is the one alcoholics have when they ingest alcohol. This manifests as a loss of control, an overpowering craving to drink more, which is why alcoholics cannot sustain moderation. That never occurs in ordinary drinkers.