I have a male yorkie about a year old. My step mother says he to small and need to eat more. But he is 5 pounds he just thin in the tummy area. Could something be wrong? Also is it OK when he gets a bath that he kind of Cold?

Only a Vet knows if his weight is appropriate. It's not good for ANY dog to get chilled when he gets bathed. How often are you bathing him?

About once a week...

You don't really need to bath a dog every week unless they are getting really dirty. I use a waterlerss bath shampoo on my dogs legs when they have been outside and get dirty and they get a bath about once a month when they get clipped.

I agree with JudyKayTee, your vet can tell you definitely even with a photo we couldn't tell because they have long hair that would cover any 'skinny bits'