How to know when baby has had enough?

BabyBlu🐼 • Mom of Irish twins
My son will be 2 weeks old on monday and i dont know how much i should be feeding him. He's my second baby and i always assumed babies know when to stop eating but my doctor told me that that isnt true and that their sucking reflex is too strong so they will continue to want to suck on something even if they arent hungry anymore. Which makes sense since my son has thrown up every single time i let him stay on the boob for as long as he wants. What are some signs or how do you personally know when you LO has eaten enough?