Using the strict definition of the word "allergic", it is really not possible for you to have an allergy to alcohol. However, there is a possibility that you could be overly sensitive to alcohol and develop stomach aches and other symptoms in response. There is no way for me to tell why you develop these symptoms. Some people who react badly to alcohol have a deficiency in one of the enzymes which helps break alcohol down. This can be found especially in the people of Asian decent. This enzyme deficiency causes one of the alcohol breakdown molecules to accumulate which can cause symptoms. In layman's terms, this just means that when people with this deficiency drink alcohol, they cannot get rid of it some of the toxins causing them to feel sick. This may be what you have.
I think that you should probably just avoid drinking alcohol if you can. This is an issue that you should discuss with your primary care physician
. He or she can review your list of symptoms and decide if there is any additional testing that is warranted. In the mean time, I would take it easy on the alcohol so that you don't make yourself sick.