I think there's a possibility you aren't eating enough fat or calories to absorb the alcohol, which is sometimes common in new vegans, at least the calories part.
There's a reason why conventional bars sell deep fried snacks, or had bowls of high fat nuts back in the day.
I would suggest that if you choose to drink more than 2-3 drinks, that you be certain that you eat first, and when you do drink on weekend or whenever you are drinking more heavily, that you opt for veggie burgers and french fries, pizza with vegan cheese, battered zucchini or mushrooms, dishes with avacado or guacamole, or a nice vegan lunch "meat" sandwich with Just Mayo...things that are calorie dense and fatty. If you are doing low fat vegan or are only eating raw vegetables, or very light food with drinking more than the doctor recommended amount (which is 2-3 drinks, in the United States). You know how pain killers say to be careful if you consume three or more alcoholic beverages a day? You should also follow that for choosing what to eat.