Why does my cat keep throwing up?

ahhh,if your kitty throws up ,especially after it eats,its a hair ball.i know,i know you said you saw one before and this isnt it, but sometimes you dont see the hair ball especially if its kinda clogging the throat,the food goes down and cant stay down.when my cats get them,they throw up,and i never see the hair ball,they may swollow it,sometimes i do see some in the litter box mixed in,ick! ha!so still try the hair ball medicine and see if it helps.