If i had a milk allergy, what would happen to me if i drank a glass of milk?

Depends: Different reactions could occur as a manifestation of milk allergy most commonly rashes (eczema or hives) or GI symptoms (usually pain or diarrhea). Eosinophilic esophagitis, an allergic reaction in the esophagus is often associated with milk allergy. Other manifestations include nasal symptoms, especially congestion, or wheezing. And the most severe manifestion of milk allergy is anaphylaxis.

Very sick: Symptoms of milk allergy include immediate hives, swelling (tongue, lips), vomiting, diarrhea, cramping, and even shock (anaphylaxis). It may not even take a whole glass, but just a tiny sip to have a severe reaction. If one drinks large amounts of milk/dairy and just has GI symptoms like cramping, belly pain and diarrhea, then likely this is lactose intolerance. Less serious but miserable.