You might want to bring in a stool sample to test for intestinal parasites. Most are not visible to the eye. Kittens and puppies usually need repeat treatments to cover all life stages of parasites. You don't have to bring your kitten in for this if it's at the same clinic you've already been to.
It's also not unusual for different scales to be off by even 1lb or more. Just a thought in case you want to re-weigh your kitty.
"Education is a progressive discovery of our own ignorance." -Will Durant