My guinea pig is sick?

[kathy lim]

my little guinea pig is sick and I have no idea what to and I i really don't want him to die. all he does is sleep. he hardly eats or drinks, i have to pick him up and force feed him. his poo is wet and yellow. i fed him carrots, cucumbers and a tiny bit of grapes. i took him to the vet and they said no more cucumbers or grapes but the carrots are fine. i stopped feeding him all that stuff and just fed him their ordinary food. i'm stressing out so much. when ever i make a loud noise he doesn't flinch or runaway when i try to pick him up. he doesn't run around the cage or anything. he just lays in one spot. his tempreture always changes from cold to warm. please help me out and give me some good advice because i'm afraid that his going to die on me.