Need advice on a couple things

I go back to work next week and i’ve been ebf on demand so when I go back I have no idea how much he needs to eat and how often. i’ll be at work with him (i work at a daycare) but cannot be feeding him constantly i have to pump for work. I’ve been stocking up on milk after feeds sometimes but only get 1 ounce -1.5 ounces after feeds. How can I increase this amount since I can only pump about twice a day right now because he soothe feeds and feeds constantly. and how often does he need to eat when i go back to work?? and how many ounces? he will be 6 weeks when i go back.