Itching in dogs can be due to allergy to flea, pollens, molds, dust, food, insects and contact allergy. Parasitic skin infections like scabies especially sarcoptes mange, Cheyletiella or lice which causes pruritus, pyoderma, ringworm infection, Cushing's disease, endocrine diseases due to hormonal imbalances, autoimmune skin diseases and and almost all skin diseases. Itching can cause licking, biting and chewing in dogs which can lead to hair loss. So, your vet can differentiate the cause and can prescribe medicines after complete physical examination and some blood tests. So, take your pug to another vet for second oinion.