BF question

My 17 day old baby isn't gaining weight or

Losing weight. He's exclusively BF and even the doctor doesn't understand. He has no signs of dehydration. He has good color, mouth is moist, and is filling 10 diapers a day plus pee is clear. I am on a nipple shield though.. could that be it? He never seems uncomfortable or hungry.. I feed him till he is like passed out or until he absolutely doesn't want me anymore. My supply is pretty good and I can pump 2-3 ounces 3 times a day. I just don't know if I'm starving my baby or not and it's terrifying