we had the same experience as you. when nanny was around she drank up till 100-110ml, but dropped to 60-70ml after nanny left. we were very worried initially and tried to wake her from sleep to drink more. but eventually she still gained weight well despite drinking less so we came to terms with it. could just be the case of baby trying to catch up in the first month then normalise after.
maybe ur baby fuss is because there is gas during in btw feeding.so ur baby asking you to help to burp.coz I also get to learn this from my LO yst.She suddenly fuss in btw feeding.After burping,she allow me to continue to feed with lesser fuss..Or either u are swaddling ur baby during feeding probably can remove the swaddle during feeding. Hope this helps you.