Baby not gaining weight

Erika • Trevizo party of 6 👨‍👩‍👦‍👦🤰🌿🦁🙏

My Sonshine is 11 days old and hasn't gained an oz since he was born. It's very frustrating because it feels like I'm breastfeeding him all day, I feed on demand and recently started pumping per Drs orders. I'm still a little confused as to how I'm supposed to feed him my breast milk and pump. Do I wait to give it to him in a bottle to build a stash? Or do I give it to him right away? I'm producing milk cuz I can hear him gulping when he feeds and he sometimes even chokes! Dr also recommended formula but I'm scared he'd rather have that than my milk in the future. I was thinking of mixing 1:1 breast milk and formula.

He went from 7 lbs 2 oz at birth weight to 6 lbs 6 oz at day 9 😔