You may have reacted to the vaccine:.when they vaccinate they introduce to your body dead virus; it isn't live virus so it doesn't give you the flu, but what the introduction of dead flu virus does is put your body defense mode so that if you contract a live flu virus your body is ready to fight it. 

Your symptoms are not the flu, they are your body going into fight mode, and because it's reacting to a dead flu virus your body thinks it's a live flu, because it can't tell the difference between a dead flu and a live. You may experience fightback symptoms for a day or so, but that's what you're experiencing...and that dead virus has RNA that will stay I your system for awhile and keep your body on alert so that if you actually contract a live flu it won't be as bad as if your body had not been prepared beforehand.