my 2001 hyundai accent shakes when i come to a stop and also when i reverse.

my car shakes when I put it in reverse and when I come to a stop. it takes a little to speed up if I put it in N it calms down. My dad recently replaced all spark plugs and I get regular oil changes., My check engine light blinks when I first turn the car on then stays on I went to auto zone and they said its a misfire detected and multiple cylinder misfire I also have a hard time starting it after i refuel i have to hold the gas petal down for it to start. please some one help no one can figure out whats wrong with my car.