twanger,
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