Jen
It's not uncommon to feel like this. Life takes on a very different pace when a baby arrives and every decision suddenly seems like life or death and can result in hours of agonising ... i've been there.
Rest assured that from what you have written here you sound as though you are doing a fab job, all the right things, and are focusing on the feeding as a "reason" for feeling down. And it's not the feeding, it's just how you are feeling - tired, overwhelmed, tired, unsure, tired, tired, tired!
Why not send out your DH to buy some formula stuff and then he can introduce some feeds at night before he goes to bed - letting you get an early night, and then when you get up in the middle of the night to breastfeed you will not be shattered? Baby will take to the bottle better from her daddy because he doesn't smell like your milk and you are not in the room (although the temptation to hover will be hard to resist!).
And like others have said, it gets better on a daily basis - and sometimes we just have days where we've had enough and just want a cry and a cuddle ourselves!
Take care, keep posting for moral support and please know that we've all been there and you will be offering support to someone in this position next year!
xx