Why do i get sick after drinking orange juice? is this an allergy?

Not necessary: Allergy to oranges (including juice) can present as itching, hives, wheezing, vomiting, diarrhea and less likely anaphylaxis. If symptoms are limited to stomach upset only, it may be only a food intolerance possibly related to the acidity. If a person can tolerate a small amount, but GI symptoms with larger amounts, this supports an intolerance. Either way, if it bothers a person, avoid.