So here's a question for you wise ones out there

Molly's boys are all energetic and nursing well. I weighed them around 11pm last night and 6am this morning. The littlest one is only 1.75 ozs - but this morning was up to about 2ozs- he was so tiny and skinny when he was born, and now has a little pot belly. He worries me because he is so small - any word of wisdom on tiny ones?
Thanks!