You were sick before you got the flu shot. The incubation period for the average flu is 5-7 days. If you got sick the next day, it wasn't because of the flu shot.Well actually I was doing fine and dandy until after I got the flu shot.
I had a flu shot about 10 days ago and my arm started to itch at the injection site immediately. It continued to itch off and on for about a week. I have yet to get sick.