Good Morning and welcome! I am Dr. Loretta, a licensed veterinarian and I am happy to answer your question.
Because of Stally's age, I would worry that there may be a mass inside his mouth that is causing this odd behavior...this will not show on xrays or lab work and will require a thorough oral exam....if this is a mass or oral ulcer, then treatment may or may not be successful.
Since Stally is not responding to the medication, more extensive diagnostics will be required to know what is causing Stally's discomfort.
Does that make sense to you?
Please let me know if you have ANY other questions. My goal is to give you 100% satisfaction and if you are not yet satisfied, please REPLY so I can clarify for you.
Sincerely, Dr. Loretta