GSDMOM, your dog sounds much too much like mine for my comfort zone. I'm certainly no expert, but this does not sound like Pano to me. Pano usually moves around from leg to leg.
We got our dog when he was 6 months old, already limping, so we don't know how long he has been lame. The original diagnosis was Pano, but after a couple of months with no improvement and his limping on the same leg, we decided to seek out another vet's opinion. The true diagnosis is tendon damage to his shoulder and lesser soft tissue damage to both elbows.
This little guy also seemed to have no qualms about running as hard as he could, jumping, playing, like nothing was bothering him. But, he always limped, so something had to be wrong and causing him pain.
He's now on as much restriction as we can manage, and we are now in our 4th month of only going out for bathroom breaks. There is no other treatment but rest.
It's easily visible which shoulder has the problem. There is absolutely no muscle on that side. The other side is nicely rounded, but the injured shoulder is totally flat. We are hopeful that he will some day be sound, but it's still going to be a very long road ahead for him, with a lot of damage to repair.
Please don't dismiss your puppy's lameness as Pano and ignore other possibilities. It might be something a lot more serious, not to say that Pano isn't bad enough.