Lazy pug; or something wrong?

Hi,
My 21 month old pug has a grade one (no surgery required) luxating patella in his back right leg.
He is afraid to go up stairs (only goes up the 4 front steps very quickly)and stops constantly (every 10 feet)when we are walking with him and our other pug. At first this was ok and I thought it to be part of his personality, some dogs are more active than others,however the fact that he never goes up to the second floor in our home despite his desire to be with us and constantly stops when we are walking for no apparent reason (apart from looking around) is troubling.
My vet has suggested trying metacam for a week or two to see if he improves, we could then assume that this behavior is pain related and address it accordingly. I was wondering of anyone else with a pug may have experienced this same problem and how it was solved. It is also important to mention that he can run and play, though not as quickly as our other pug and when at the dog run prefers to just hang out and casually stand or sniff up other dogs.

My dog has grade 1 luxations in both rear legs, one is worst then the other because it popped out quite badly at one point and has never been the same.
The vet said if he isn't in pain then he doesn't need surgery. He never acts like he is in pain even when he hobbles on 3 legs (cold weather makes his legs worst from shivering/tensing) Be he still chased squirrels around the park like mad.
We walk for KM's and be never slows down.
There is no harm in trying the pain meds and seeing if his behavior improves, but he may just be stubborn and lazy. I have definitely met some pugs, they have a huge variety in personalities.

Thank you. Will contact the vet regarding testing out the situation with Metacam just hope my boy is not in pain and that I am not pushing him to hard by trying to get him to walk. Will also cut down food as he has gained 2 lbs owing to his lack of exercise.