When you first get the symptoms they come on fast and strong not gradual. Typically symptoms last 3-7 days and you feel so bad all you want to do is lay in bed.
If you think you have the flu try to see your health care provider within 48 hours of the onset of symptoms. He/she can preform a flu test and diagnose you based on symptoms and physical examination. You may be able to take an antiviral medication to shorten the duration of the illness and lesson the serverity of symptoms.
Get rest, stay hydrated and stay away from people so you do not spread the virus.