Breastfed baby not gaining weight

My baby is 11 days old and he only lost 2.9% of his body weight during our hospital stay, much lower than the acceptable 7-10%. My milk came in quickly and a lot of it. I can hear him swallowing, he has a lot of stools and pees throughout the day, he feeds for at least 20 minutes at a time and at least the recommended 12 times a day (every 2-3 hours) but he isn’t gaining weight, or at least not a lot. We left the hospital at 8lbs 4oz and at 11 days he’s at 8lbs 6oz. His original birth weight was 8lbs 7oz. My daughter had the same problem only with her I was a severe under producer so she ultimately switched to formula entirely.

Anyone else experience this?