A physio will give you exercises to do that will build up the muscles to support the joints- so the muscles do more work and the joints less. Because he will be walking abnormally due to the pain ,it puts strain on to muscles not normally used and can cause them to spasm etc causing more pain. Physio relieves the spasm, and can help with improving the range of movement for the joint.
They also use hot and cold therapies and lasers for pain relief.
As a vet nurse, I don't fine NSAIDs like Meloxicam and carprophen )the drugs you have tried) work well for arthritis pain, a paracetamol and codine based drug like pardale-v seems to help a lot of dogs when the others do not. Also Tramadol is an opiod (like morphine, but not as strong), it is very good for moderate to severe arthritis pain. another new NSAID Trocoxcil works a bit differently and we have had very good results with it- it is just a tablet a month.
You need to get on top of the pain wind up- hit it hard with strong drugs for a week or two, then you can taper them off and use a mild drug as maintenance unless you have a flair up etc.