baby dropped on the growth chart.

Mariah
So I've twins. The first two months I exclusively pumped for both of them. Then my daughter started nursing. I kept pumping for my son until New Year's Day he started nursing too. However today we went to the doctor and he didn't lose anyway but he didn't gain any in a month and a half. I feel like a awful mom for him not gaining. He has been in the 50th percentile since he was born but he's dropped to the 25th now. I don't know if I should start pumping again or start supplementing with formula. I feel so lost. I love nursing my twins but what if my milk just doesn't have enough calories for them. My son was born with Down syndrome maybe his latch just isn't strong enough to get all the milk out. I'm not engorged so I thought he was getting enough but the doctor said "I don't think he's eating as good as you think he is" and that killed me today. He also is more then likely going to have to have open heart surgery soon and I want him to be as big and strong as he can for that. Aaahh. I don't know what to do. What would you do if you were me? S