Are you sure it's the flu? People often attribute common colds or other illnesses to influenza, since everything causes similar symptoms.
Don't believe that crap about flu shots being dangerous. Some years they're not particularly helpful, but they're not dangerous (unless you include 'sore arm' and some temporary flu-like symptoms). I get seasonal flu shots, and don't get the flu after (that said, if you're anxious about them then don't get the shot and just avoid contact with people who can actually die from flu until flu season is over).
With any infectious disease, the best preventative strategy is to wash your hands obsessively, avoid doorknobs and touching your face, and make sure you're not deficient in nutrients. I don't believe a good diet will solve all your problems, but it certainly can't hurt.