How much to feed a 1 month old? Please help!!

I’m a FTM and my son will be a month old on Wednesday. He eats 3oz every 3-4hours but sometimes eats before the 3 hour mark. I’m afraid to give him 4oz bc when I did one time his stomach got really hard and he spat up a lot and started spitting out formula. But the issue is, is that no matter how much I feed him or how frequently he’s still hungry. He’ll smack his lips, root around, mouth at his hands. I asked his pediatrician and he said to feed him however much he wants until he’s satisfied but he isn’t ever satisfied and I don’t want to cause a stomach ache.

His formula is Enfamil Gentalease and I pace feed him so he won’t gulp it down too fast. Any advice is welcomed! Thanks (: