Hello & welcome, I am Dr. B, a licensed veterinarian and I would like to help you today. I do apologize that your question was not answered before. Different experts come online at various times; I just came online, read about your wee one’s situation, and wanted to help.
I am very sorry to hear that Tucker is suffering with these painful episodes. If the xrays were normal, they do rule out a lot of issues (ie bone based tumors, spinal arthritis, vertebral malformations or misalignment), but the lack of findings does mean that we have to be very concerned about what may be going on inside Tucker's spine, neck and even brain. Any compression (from swellings, protruding discs, infection, bleeds, tumors) could cause these intermittent fits of pain.
In regards ***** ***** here, the pain relief is important for him. If you don't feel that what he has been given is enough to control this; then do ring his vet to discuss other options to use (alone or in combination) so that you can get him comfortable. Otherwise, it may be worth discussing referral to a specialist veterinary neurologist for further diagnostics. In cases like this MRIs can be of particular use to allow us to see inside the spine and skull to pinpoint the root cause of his pain. And once we know what is present, we would be in a position to treat it appropriately and get him back to being the comfortable dog you know.
Just in case you wanted to check for the veterinary neurologist near you, you can check the ACVIM database HERE (do click "neurology" as the specialty). or your vet will be able to advise you of local options.
Please take care,