Aw, I'm so sorry to hear of your baby hurting like this
. I don't know a whole lot about arthritis, but I was going to suggest Cosequin - and you're already using it. There are a lot of things they use in humans, so many more options it seems - did the vet offer nothing else? I wonder if there is a specialist you could consult with. What did the vet say about it showing up so early?