Try carring some Meti-Cam
Metacam is Meloxicam (generic). Metacam is the dog drug that costs a mint, Meloxicam is for humans. Ask you vet to write a script for the human meloxicam. You can get it through Walmart, Target, etc for $3/30 pills. Metacam is $80-100/bottle.
I have a ton of this in my supplies. It is a wonderful anti-inflammatory. If your vet will do this and most will, ask for the 7.5mg tabs- this should work for your Lab. Splitting the 15mg tabs is a pain.
I was going to recommend this for your dog when he was having off days. Cheap, works great and your dog will be happier.