I have a new yorki poo- first time dog owner, i'm paranoid!?

my puppy is the best. but he's so sleepy and always looks depressed. been the vet for his checkups and they say he is fine other than giarida- but he's on meds for that. and he is also on meds for kennel cough which is cleared up now. but he mopes around. i take him to work with me and he's in an office - but with tons of toys etc. is there something wrong with him? even when we go outside to "play" he sits down!!!!