Question about a Kitten?

My kitten is 14 weeks old and I just got him from a shelter on Friday. I took him to the vet today and everything checked out, but he has ate very little hardley anything since i brought him home. He also sleeps all the time and is only awake for about 20 min out of the day. He doesn't play at all. Everything came back neg from his bloodwork and he is not anemic. I have also tried all different foods dry, soft and some the vet gave me.Any ideas I am pretty worried. thanks