Yes if it has been four days and he is still having a hard time with the head shaking and balance then it would be best to have him seen for an evaluation. This could be the result of a neurological disorder if the antibiotics have not helped and he is having problems with his balance. This can be known as feline vestibular disorder so it would be good for you to take a look at his eyes and see if he is showing any abnormal eye movements as well as this can also be a sign of this type of neurological disorder. It also may be that he needs a stronger antibiotic or that this is related to mites so if you see any black specks in his ears that can be a sign of mites and that causes head shaking as well but not usually a problem with balance. With the balance problem you are seeing it sounds more like a vestibular problem to me. Here is a good link that will explain more about this disorder.