How do you know if you've run out of milk at end of day?

Dd last night was constantly wanting to feed but would keep pulling off like she was frustrated nothing was coming out she screamed until 1am! When I was finally able to get her to sleep in her rocker , I know I didn't drink much water yesterday because I was nauseous

I'm feeling frustrated because she's usually fine but when she has a fussy night where she won't stop screaming and feeding dh starts nagging about formula feeding because ds was alot more settled on ff

I do often struggle to drink enough because It seems impossible to remember or get the time when I'm split between 2 kids