When does the milk really come in?

Laura • My partner and I are expecting our first together in January :-)
I started having to supplement my son with formula because of jaundice and needed him to poop more to get the bilirubin out of his system. Now the doctor is keeping him on it because he hasn't gained enough weight bc I am not producing enough milk to feed him. He is only 6 days old so I know it's early. Everyone is telling me give it time, it will come in. I am not on a schedule where I feed him every 2.5 hrs then pump right after to stimulate milk production. If I get half and ounce total it's a lot.