Why does red wine give people headaches?
Is it from drinking too much? It can be.
Is it sulfites? Probably not.

Have a look at this from Food and Wine

“Dr. Sami Bahna, at the Allergy & Immunology department of the Louisiana State University Health Sciences Center, explains that genetics (and certain medications such as MAO inhibitors) may impair some drinkers’ ability to metabolize histamine and its brethren. This means more amines make their way from the belly to the bloodstream, which can lead to symptoms such as facial flushing and, indeed, headaches.“