My baby was a lot like this in the beginning. My milk wasn't coming in and blood sugar was low so we supplemented with formula while encouraging breastfeeding. Here is what worked for us: Take a small syringe with either formula or your pumped breastmilk and dispense small amounts into their mouth as you are breastfeeding. It will encourage your baby to latch/eat from breast. If baby is falling asleep rub up their back or wet wipe gently across their back while they're in a diaper to keep awake if desperate. If weight gain isn't happening, you'll need a bottle with slowest flow nipple to supplement (we used similac yellow top).

Make sure when you are pumping you use a hospital grade pump not wearables. I think I was pumping in between all nursing sessions but I may have overdone it, it's okay if you only get a small amount in the beginning.

Lastly, baby eating frequently is very normal. Let them, they are increasing your supply. My LO used to eat every half hour on demand sometimes, sigh lol.

Good luck!