Won't latch and easily frustrated

My boy who was born early and had to suppliment within the first few hours bc of low blood sugar won't take a deep enough latch and gets easily frustrared. My pump that I bought through insurance hasn't arrived yet and I am super engored which of course doesn't help the latch. I am serious concerned that he won't breastfeed and I will have to pump exclusively like l did for my daughter. That situation would be hard this time bc I have two kids now. Do realize that it's only day 3 and I have time for help but it is overwhelming. Why is this so easy for some?