Breastfeeding help!

FTM here. So my baby is almost three weeks old and he's just now gotten back to his birth weight. I'm exclusively breastfeeding and I'm worried about his weight gain. He had his first appointment today and his Pediatrician is contemplating having me supplement. I have a week to get his weight to go up a bit before she wants me to. I am most definitely producing so I know that's not a problem. I really don't want to have to supplement so is there anything I could be missing? I feed him every two hours and on demand in between. Should I feed him more? Do I try to have him drain both breasts? Is there any way to "fatten up" my breast milk? Help!!!