That's good to hear. It's always uplifting to have a vet pronouce them healthy. I just think that as a young puppy no one played with him. Perhaps if you sat down and spent time teaching him to play that he would get into it. Just a suggestion...
Kacee is just past 6.5 months old and while she sleeps all night, she sometimes takes a short nap in the morning, then in the middle of the afternoon she usually sleeps a couple of hours, then naps about an hour and a half after walking and playing at night before a little more play before she goes to bed for the night. She has more or less developed a routine now. She spends a great deal of time outside playing in her yard.