Alcohol intolerance. Common symptoms of alcohol intolerance are nasal congestion and skin flushing (not a true allergy). Alcohol intolerance is caused by a genetic condition in which the body is unable to break down alcohol. An allergy is possible to a component of the beverage— such as chemicals, grains or preservatives. Another rare cause is hodgkins lymphoma. The only treatment is avoidance of alcohol, sorry.
Why do you keep. Drinking it when it makes you sick? Some people are very sensitive to alcohol effects, or it could be some other ingredient in the beer. You might be gluten sensitive, and most beers are high in gluten protein. Talk to your doctor about it. Do you get sick with other alcohol-containing beverages, or have you tried "non-alcoholic" beers to see if the same kind of reaction occurs.