Hi Im also new here and had a similar problem.I soon realized from other YTers, that bringing home such a tiny baby is not advisable until their older..When I bought my puppy home she started eating less than usual.My breeder told me she was a good eater and I knew it because I could see she had a big fat belly.After she came home she only ate a few kibbles and her belly was always flattened.I was so worried.After a few days she became accustomed to her new environment and she started to eat again.I also changed her food to something she liked better.I posted a thread it may be helpful.A member (drawlins27) gave me a good idea and it might work.Its a mixture she made to feed her tiny 8 ounce baby.scroll down and look for it.
http://www.yorkietalk.com/forums/showthread.php?t=93395
Dont worry,Im sure your baby will be fine.Make sure to keep us posted .