I always feel a little ill after the flu shot, why is this?

Normal Reaction. This is a normal reaction to the shot, the viruses in the flu shot are killed (inactivated), so you cannot get the flu from a flu shot. Some minor side effects that could occur are: soreness, redness, or swelling where the shot was given fever (low grade) aches if these problems occur, they begin soon after the shot and usually last 1 to 2 days. - cdc.