While vets are not cheap, they are a necessity. If you are not happy with the one you have, maybe put some feelers out for another.
Personally, if my pup were acting like you are describing yours, I would want a diagnosis. Sounds like the Metacam helped his discomfort, but you still don't know why he is having pain. You might be able to fix whatever the problem is rather than masking it with medicine. Maybe not....but worth finding out imho.
By the way...welcome to YT!