I am sorry to hear that your fellow Ozzie is having trouble chewing and eating and seems to be drinking more than usual.
I understand his veterinarian examined him and did some blood tests, showing mild elevations in his white blood cell numbers. If the antibiotics were going to help I would think that they would have done so by now.
Is his jaw hanging open all the time?
Or can he close his jaw but is unable to chew or bite down with any force?
Or is he unwilling or unable to open his mouth?
Is he in pain?
If he is unwilling or unable to open his mouth we need to consider disease processes that affect the muscles that control chewing (masticatory myositis) or his temperomandibular joint, or an abscess up behind his upper molar that makes opening his mouth and chewing excruciatingly painful.
If his mouth is hanging open, and he cannot seem to close it or chew, then nerve inflammation/damage of his facial nerve may be the cause.
Your fellow needs to see his veterinarian for a recheck. They will likely want to try getting him to open his mouth fully. If that isn't possible then sedation to see if his muscles relax and it is possible to open his mouth. If not then radiographs of his temperomandibular joint,jaw and skull, and a biopsy of his masticatory muscles (chewing muscles) could help with a diagnosis.
In the meantime he should be on fluids. You can blenderize canned dog food and broth to make a puree that he may be able to lick up. Or you can try some meat baby food. Ideally he should eat dog food, but he needs to eat now after 4 days of getting little to no food, so whatever we can get in is great.
Please let me know if I can be of further help.