To me Jack still seems thin. He's approximates 8-9 weeks old and when he went to the vet a couple of weeks ago he weighed 2.3lbs. The vet didn't seem concerned that he was too thin, but I can really feel his ribs. He gets plenty to eat throughout the day. I always thought kittens were kind of pudgy and he's not. He's been wormed also. Should I be concerned?