Thanks for all the replies - I am so worried about him. I baby him when he's not hurt, so he is getting lots of extra pampering now! That made me laugh to hear about Bella wiggling for Sammy

Hopefully, he'll feel better soon and can come back to the dog park to play.
I talked to my trainers at puppy class tonight and they recommended a vet visit in 2-3 days if he is not doing any better. By the way he was shuffling his back leg and really limping in the trot, they were worried about a cruciate injury
I will keep a watch over the next few days and hopefully will see some improvement. Samson is not very happy having his exercise restricted. It breaks my heart to see him hurting.