OK so my little man isn't gaining weight. He is 3 weeks old and 6lb. He was 6 12 at birth. II have been breastfeeding mostly and the weird thing is he is having enough wet and poo diapers. But the doctor (vary pro breastfeeding ) was sad when she told me to start supplementing. She is also confused as to why he's not gaining if he's potty enough. Did anyone else have this problem I breastfeed as much as possible and always give the breast first than offer the bottle. (Usually if he drinks the bottle (formula ) he spits it up) we go to the doctor for a weight. Check in the morning.