17 year old female. taking allegra (fexofenadine) for chronic hives, but have been feeling very nauseous. could allegra (fexofenadine) be causing the nausea?

Possible but: Any drug or food can cause nausea for some people and thus it is possible. However it is not a common side effects from allegra. I would suggest that you stop taking Allegra (and try another otc antihistamine which is not fexofenadine) for a few days. If the nausea continues, then you should consider seeing a doctor. Do remember that even urinary tract infection or pregnancy can cause nausea.

Discontinue allegra (fexofenadine) : discontinue Allegra (fexofenadine) to find out if nausea is related to Allegra (fexofenadine). if yes, choose some other antihistamine for chronic hives. if not, retake Allegra (fexofenadine)