Help please

I have never been able to produce more than an ounce out of each breast with both my kids. My first child breastfed until she was two but the first 9 months we did formula and breastfeeding. Now my second is a month and it’s the same.

I have tried power pumping 4 times a day for a week and putting baby on breast between. I eat oatmeal for breakfast every morning. I drink 4 litres of water a day. I take my iron pills. Tried the drinks and teas. I tried it all. For some reason I just don’t produce. We know I don’t produce more because I did multiple weighed feedings with both and both my children lost too much weight until I introduced formula.

I slept through the night on accident one time and got 4 ounces out of each breast so I know they are capable of holding that much. They just don’t produce that much every 2-3 hours.

I have no idea what to do. I feel like there’s something wrong with my body. Any advice to help my supply or medical reasoning why I can’t produce more?

*sorry should have added baby nurses every 30ish minutes and I alsopump every 2 hours for 20 minutes. He gets everything I pump plus formula. He’s gaining appropriately now that we’ve added the formula top ups. He lost over 10% body weight by a 2 weeks.