I started taking Zyrtec (cetirizine) for 3 days, scratching issues, I have an event where I want to drink if I don't take the pill for one day may I drink alcohol?

Drink HOW much ETOH? I always assume when someone asks a question like this that they are not talking about one or two social drinks. There is really no significant interaction between alcohol and antihistamines like zyrtec, (cetirizine) although both may be sedating. However, alcohol itself can result in itching, and may be part of the problem. If you are talking larger amounts of alcohol, that is in itself a problem.