He is still very young. My Marcus Aurelius wouldn't eat when we brought him home for the first almost three weeks. It is important that if you feel he isn't eating enough that you take him to the vet again. I know how you feel when you say that he has been at the vets more than at home. Marcus lived at the vets for the first almost two months we brought him home. We almost lost him... But they do come around in time and start to play more. Don't worry about all the sleeping, babies need lots to sleep to grow up big and strong
. I would also take the suggestions of the other posts here to find a food that your furbaby will eat. The greatest sight you can see after going through something like this is to watch your little guy eat like a little piggy
Hope this helps and congrats with your newest addition to the family!