is baby getting enough?

Miranda

my son is 16 days old today and we have been on a rollercoaster with breastfeeding. the first week he exclusively breastfed, then the doctors weren't happy about how long it was taking him to gain his weight back so they told me to supplement with bottles of pumped milk after his feeds. he started gaining again and so we phased the bottles out and i've just been exclusively nursing again with a breast shield (which seems to really help him transfer the milk more efficiently). i will let him nurse for 30-40 minutes and he will fall asleep, his arm will be floppy, he will reject the breast, and then as soon as i go to lay him down or give him to his dad, he starts putting his hands in his mouth again. should i be cautious about nursing him for too long? i don't want him to be burning more calories than he is taking in. my IBCLC also told me if i offer him a pacifier and he calms down and settles then he is likely not hungry, but if he won't settle with the paci then he may still be hungry, is that correct? i'm anxious about the pacifier trick cause i also don't want to mask his hunger cues.. but it makes sense. what are your alls thoughts?