I have done whatever is recommended for fleas yet my poor dog is still scratching itself to bits. What else can I do?

Can’t be food allergy, I see the fleas have gone but she is still scratching away! I have tried whatever is on the market as well as coconut oil. Dies down for a while and starts scratching herself crazy! I am really careful and take impossibly good care of the dog and it hurts to see her so irritated. What else can I do before vet starts oral treatment?
Her coat is in excellent condition, no skin problems or “dandruff”. I don’t see what could be wrong!