How old is Buck? How's he been eating and eliminating?
Couple things to think about too, he just left his litter mates, he's in a new house and you aren't momma yet. They're going to be a little bummed at first.
My boy took a couple weeks to fully warm up to me and my wife. We got him when he was 12 weeks old, so that could cause a little more seperation issues with his family. He's a part of our family now 100%.
EM pups love to sleep, no question there. I wouldn't worry too much about it right now, it sounds pretty normal to me.
Edit:
Duh, just noticed to said his age! Sorry.