I never got a flu shot, even though its free here. I always seem to catch it once or twice a winter.
I highly doubt you've ever had the flu if what you're getting sick with once or twice a year is what you're calling flu.
Until I caught it a couple years ago I wasn't clear either. You hear about the flu all the time, assume you must have had it at some point, right? And maybe so, some years the strain that comes through isn't so bad, sometimes like this year it's really nasty. But after getting it I regret having ever called a cold the flu.
When it feels like you're taking a deep drag on your 200th cigarette of the day every time you take a breath, when you're exhausted tieing one shoe and need a five minute break before attempting the other, when you're in a permanent crouch so the coughing doesn't hurt quite as bad, when you have to sleep sitting straight up because any incline makes it too hard to breathe and when a sip of water is a meal, then you have the flu.