When I take medicine that has ansaid (flurbiprofen) in I get a really bad headache, am I allergic to ansaid (flurbiprofen)?

Probably not. Based on studies, the most common nonsteroidal antiinflamatory agents (nsaids) side effects include: nausea; abdominal pain (stomach pain); heartburn; dizziness; an unexplained rash; constipation; diarrhea; gas; vomiting. Side effects of nsaids that require immediate medical attention, include chest pain, shortness of breath, or weakness on one part of your body (possible stroke or heart attack).