Is my Labrador under weight?!

Hello All,
I have a 15 week old lab, we did pick the smallest out of the litter we just fell in love with her. But I do have some concerns about her weight he is on dry food at the moment after every feed her belly will bloat out then after an hour or two he looks really skinny again? Anyone help please? Should we be feeding her differently?
Please help.
I didn't find the right solution from the Internet.
References:
https://www.petforums.co.uk/threads/is- ... ht.478477/
Cryptocurrency Animation Video
Thanks
I have a 15 week old lab, we did pick the smallest out of the litter we just fell in love with her. But I do have some concerns about her weight he is on dry food at the moment after every feed her belly will bloat out then after an hour or two he looks really skinny again? Anyone help please? Should we be feeding her differently?
Please help.
I didn't find the right solution from the Internet.
References:
https://www.petforums.co.uk/threads/is- ... ht.478477/
Cryptocurrency Animation Video
Thanks