he's ill =[

my chinchilla is ill, and i mean really sick. he wont eat or drink and squeaks when i pick him up like its hurting him, even though im being as gentle as possible.
iv been to the vet but the medicine is making no difference, hes lost weight and become exahusted, all i want to do is make him better, and id do anything for him to make it.
i know animals get ill, but i feel like i have done something wrong, even though my other chinnie is fine, and iv treated them exactly the same.

i just cant bear to think he might die.
=[
xxxxx