When i drink alcohol nowadays my head hurts.. could i have become allergic to it?

It's not "allergy": Allergy really means activity of our immune system, and that isn't what this is. Alcohol causes headaches in MANY people, and sometimes the reaction is not only from the alcohol but other substances in the beverage, like nitrates in wines. People with migraine are often highly sensitive to these effects and may routinely get headache. Stop or cut down, talk to your doctor.