Breastfeeding gone wrong

So after giving birth my little lolo had to go to NCU because of trouble breathing, the hospital did not say why, but it was better after few days. Later my lolo hadn’t gain enough weight and the doctors said it was normal because of first month not many babies gain a lot of weight. The second month the weight was approximately the same. So I went to another doctor and discovered that my lolo had a phlegm inside her nose and throat that prevented her from breastfeeding the amount she needed to. When she was breastfeeding mostly she would fall asleep after short while and I had to wake her up, I thought she was full, eventually I switched to formula as my breast milk is not enough for her.

Now I only pump once and I don’t know how to increase my breast milk because she cannot breastfeed.

Any thoughts?