Hi there, I'm sorry you're having trouble with your little one.
Causes of Hair Loss (Alopecia) in Dogs
Here's a link I found that lists possible causes and treatments for hair loss in dogs. I definitely think that your vet could have ran some tests to rule out any SERIOUS underlying causes. How does he know it's not due to allergies or something? Treatment may not work if you're just treating the symptom and not the underlying cause of the symptom.
This link does say that alopecia is characterized by patches of hair loss especially on the head, neck, and body; no itching - does this sound like what your little one has? It also says that the hair usually grows back spontaneously.
I hope everything works out okay!