Why do I have such strange reactions to alcohol?

Every time I drink alcohol, I experience these reactions; I become very flushed and have fever-like symptoms, where I'm very warm but shiver almost violently. I get extremely nauseous within the hour, and throw up. My heart rate increases ridiculously and sometimes I even get congested. The more concentrated the alcohol the worse my reaction is. Could I possibly have an allergy or am I just really sensitive to it or what?