Increasing breast milk

How can I increase my breast milk supply? I eat empty calories and try to remember to drink water however I forget to take care of myself as I put our two toddlers and 5 week olds needs above mine. At max I eat maybe 2 meals if that and 2 cups of water. How do you mamas of three or more children or mamas with two toddlers plus a newborn do it?

TIA

Edit: I was pumping every 3 hours day and night but pushed it back to every 5 hours as baby is sleeping longer at night. We are supplementing with formula.