assuming that you do indeed have the flu now (lab confirmed influenza) this would not be uncommon. this years flu strain (i don't know which vaccine you received) is only about 50% protective so you can still get influenza (hopefully a milder case than if you were not immunized) since the flu virus has changed (this occasionally happens). you are never contagious from the flu vaccine of course but if you truly have influenza now you were contagious about a day before you knew you had the flu and several days to a week after you get influenza. children may be contagious for a longer period.
how long are you contagious from the flu. . i got a flu shot a month ago and i have the flu now