Cant help with the Australia referrals. I get a good bit of my pain suppressed from an old school med, amitriptyline. I also take Mobic for joint pain/osteoarthritis. I found Tramadol to be useless. Hydrocodone does work for me though for break through pain I can’t tolerate.
Flank pain could be referred pain. Does he have sacroiliac issues? Lumbar back issues? Have gastro issues like gluten sensitivity/Celiac, food allergies, IBS, gastritis, delayed stomach emptying, etc? Also, I had flank pain when I still had my gallbladder. Just a thought.