Flu shots are made a year in advance so they have to predict which strain will be most prominent. The flu virus that you're suffering from is probably different from what the flu shot protected you from. Or, your flu shot could have worn off by now. Flu season is officially over around March, and the vaccination tends to only last around 6-8 months or so.
Also, if you have the actual flu, antibiotics won't help because the flu is a viral infection, not bacterial. Do you have an infection instead?