Breastfeeding Frustration

I am a FTM. I have a 6 day old who was born weighing 5 pounds 7 ounces. Due to his low weight and mild juandice, I have been supplementing breastfeeding with formula since day 1. I don't mind doing that since it is in the best interest of my child, but my milk has since come in and I feel like I'm just not producing enough for him so I have to keep supplementing. The 2 breastfeeding sessions I didn't need to supplement lasted 2 hours. I have no idea what my supply should look like at this point or if it's normal for him to need to nurse that long. Even with pumping, I don't seem to be getting a lot. During the night feedings, I find myself having mini breakdowns over not being able to supply him with enough. I don't want to give up trying, but I really have no idea what I'm doing. I have an appointment scheduled with a lactation consultant next week, but was wondering if anyone had any advice on getting a good supply, weaning supplementation, or just surviving this period without losing my mind.