usually after a flu jab people feel a little like they have a lower immune system. It's because what they put in you is a strain of flu to make your body recognise it and immediately fight it and form antibodies. So its not surprising you feel a little sick. Although its quite a long time for your symptoms, but then if you think flu can last over a week, so this is probably what you have. If it carries on i would go get checked out by your doctor. Good luck
funnily enough he didnt use it this past winter either as it was quite a bright one. But im thinking he will be using it again this coming winter as its starting to affect him already. He has used it for one whole winter 2 yrears ago and it definetely worked.