one reason would be that you misdiagnosed yourself as having influenza. influenza in this season can be caused from one of three different viral strains resulting in high fevers body aches headaches pneumonia-like coughing etc. influenza is a respiratory viruses but there are about 200 other respiratory viruses that have the potential of causing flu-like symptoms. my guess would be that you did not have true influenza (unless your illness was confirmed by a lab test) but rather one of those 200 or so other respiratory viruses. did you get a flu vaccine this year?
last week i had the flu a week later i had the flu again but worse. why would i get the flu two weeks in a row?