Stressed mama, new to breastfeeding - Please help!

I’m new to breastfeeding and confused on what to do.

My daughter is 7 days old and I feel like her eating habits aren’t good. She doesn’t latch for long and then goes a long time between feeds. At first I thought maybe I had quick letdown (i think I did with my first - I pumped with him and was filling the bottles within like 3 minutes every time) but then she also started to projectile vomit every time and got diagnosed with acid reflux so I’m worried she’s just not getting or wanting much as a result of it. Her pediatrician doesn’t want to do much until she loses weight. But I’d obviously like to avoid weight loss, so does anyone have experience and things that helped their baby? And to help keep supply up, should I pump?