It is really hard sometimes, I had a hard day on Wednesday.
You need to eat and drink to keep your milk up.
Have you tried swaddling your DD? That has been our saving grace with DD once she started getting fussy. Swaddling and rocking her or walking around with her while gently jostling her and patting her bum.
Also, I have found sometimes that when DD seems like she wants to nurse- i.e. latches on but then moments later pulls of screaming that she doesn't really want to nurse. She is looking to that as comfort but doesn't really want the milk. It is during these times that I get a fresh diaper on her, swaddle her up and then go rock her or walk around with her. Then once she is calmed down I might try and nurse her again if I think she wants it but a lot of times she falls asleep.
And sometimes she just wants to sleep on me/ with me. I just have to remind myself that taking care of my baby is the most important thing and that is she needs me to lay cuddled up next to her while she sleeps, even if I can't sleep right then, then that is what she needs and I just need to do it.
But those days are rough. But yes, please eat and drink! Like someone else said, don't let your baby CIO but if the only way you can get some food and water is if she cries for a few minutes, if you really don't have anyone else to help you, then so be it. You have to eat and drink to be able to feed her.