This is a tough one to have for a first medical problem to handle. I would call the vet and tell him that he is starting to howl and maybe he needs something for pain too.
If things get too bad alot of us have had to make that decision for our older dogs when they can't do it for themselves
and we will understand. I would make sure he is out of pain though. Just wish you could see if the meds work but you are there with him and know best.