Hi there and welcome to YT!!
I have a tiny girl and she is very healthy so try to think positive ok.
I'm glad you joined YT because so many people on here can help you.
Your baby is really young and in my opinion way too young to have left mommy. However, you have this baby and just need to be extra careful. Make sure your little one is eating every few hours. Also, I would give nutrical daily just to be safe. Not saying you have to continue this aways but at this point I think it would be a good idea. However, keep it on hand always. I know someone that got a yorkie at 5 weeks and the baby is now 13 weeks and doing wonderful. She went from less then 1/2 a pound to now 2 lbs.
I wish you all the luck with your little one.
Please feel free to message me if you have any questions about anything. I'll try my best to help you.