If you become infected with the flu virus, you will usually feel flu symptoms one to four days later. Some of the more common symptoms include fever, muscle aches, dry cough, and sore throat. People often confuse cold symptoms with those of the flu. However, cold symptoms are usually milder and don't last as long as flu symptoms. Although nausea, vomiting, and diarrhea can accompany flu symptoms, especially in children, gastrointestinal symptoms rarely occur. The illness that people call "stomach flu" is not influenza (the flu).