Why is my chinchilla destroing his own fur?Please i need help?

hello my chinchilla that si 3 years old is picking off his fur now he has none on front legs and neck side i went to the vet and he gave me some spray to spray on his skin.now he sems like he is worse then yesterday he stoped eating and i fell like is all my foult i would apreciate if a person that has a chinchilla or is a raiser can help me i am not from usa and our medicie is so diffrent here but i need some real help cause i fell like i amloseing my baby and that makes me so crazy.tk u