How can i differentiate between the flu and a sinus infection? i gave had the flu before with no fever

Usually need a test: To tell if a person has the flu, he needs a rapid flu test which is a swab from the inside of the nose (deep in the nose), and takes 10-15 minutes to get a result. It is pretty accurate during the first 1-3 days of flu symptoms, and is very helpful in deciding what medication should be used. For people without high fever and muscle aches in flu season, it is not that easy to guess who has the flu.