Hard to understand a baby

Hey y’all 💖

I’m a teen mom and it’s been a months since my c-section

I got my lovely little daughter on 4 june. I’ve always had problem to understand if she’s hungry or not. From the very beginning she’d put her fingers in her mouth and start sucking them. She sucks everything that touches her lips, so I put her on a pacifier (so she doesn’t get a habit of sucking her fingers). She drinks more milk and then vomits it out. I don’t know how to give her milk. Sometimes the supply from my breast is more sometimes it’s less. She keeps on sucking until she’s deeply asleep and then burping is a big ass problem. How do I know she’s full? She always wants to suck something.