Baby will be here soon and I’m nervous…

So I’m so nervous to have my baby because I’m so scared I’m going to be frustrated all the time. I’m a nanny and I get frustrated really easily (I think right now it’s cuz I’m pregnant and uncomfortable) I know this can also be because they aren’t my kids and I can’t really discipline them. I have never ever done well with little sleep and I know that is what will be happening with a newborn. I don’t want to waste my time being frustrated all the time. I want to be able to enjoy the newborn stage. I know it will be hard. Anytime I get really frustrated with the kids I nanny and I react out of frustration I literally feel guilty for days. I don’t know how some moms have so much patients when kids are screaming. Any advice from anyone who has struggled with being easily frustrated.