Breastfeeding question

I know they say the more you pump the more milk you get and also as your baby grows your body will produce more but my question is how does your body just know? My baby is eating a lot for only being two months and just now he woke up and ate 9 oz! Usually he does about 3.5 and then later in the day will want about 5 but he just finished 9oz. I’m worried my boobs are not going to be able to keep up cause he is going through my stash like crazy and I keep pumping but each time after the first I only get about 2oz out of both boobs. I just want to know when my body will finally get the idea I’m needing more milk.