I have a male shar pei, who hasen't eaten for 5 days now. Hes been to the vet but still isn't eatting. Help??

Hes had some booster shots at the vet and was sent home to see how he goes... He spewed up bile and hes worm tablets that were given to him. He is still just sleeping all day and refuses to eat. I'm getting worried about him as hes getting very weak and losing lots of weight. How do we get him to eat again?