During the early spring months, there are a variety of illnesses that are circulating. When you have an upset stomach, it can be easy to automatically think food poisoning. However, there are a variety of different conditions which can cause you to have an upset stomach. Identifying what exactly is causing your symptoms can be difficult without a medical diagnosis. Norovirus is a gastrointestinal virus that causes severe symptoms like vomiting and diarrhea. Learn more ...