No puppy of mine that age slept and slept and slept or gave me the impression she'd sleep all day if I weren't around to wake her. They'd play vigorously for a while, sleep for a while, play a while, sleep a while. At 4 months I think all of mine were sleeping or at least quiet through the night, but I can remember waking to see one on her back, quietly playing with her own front feet. At 4 months they were going to puppy kindergarten, 40 minutes to get there and an hour-long class. Maybe they slept on the way home, but were sure to wake when we got there and go for a potty walk before back in the house. I second the idea that if this puppy hasn't had a thorough check out by a vet aware of its sleeping all the time, it should have just that.