Is my baby overfed?

It could be she has a stomach upset and gassy. And yes 3.8kg for 1 month is fine. My daughter 2 month weighing at 4.6kg. She does sometimes spat alot of milk too. Her FM intake is 100 ml but most time she BM direct latch. You can reduce milk intake for time being, do tummy massage, always properly burp baby to release gas, seat baby in a proper position during feeding.

Your baby may have reflux. My boy has a bit of a reflux too. So I have to hold him upright for at least 10 minutes even if he burped in between. You might wanna try that. You can also add a bit of ridwind in the day and evening just to help with the gassiness, so she is less fussy. Hopefully all these help!

My baby is 1 month old, 3.4kg. She is fed 80ml every 3 hrs and i am struggling to make her burp, even after trying different position. The past 2 days she have been vomiting at least 2-3 times. I am worried too and unsure if that is ok. No signs of crying or in pain though.

https://s.shopee.sg/AUdhlPS0nN you can give ridwind to baby to help her burp better. could be because she's gassy but she's still too young to let out gas by herself that's why.