Breast milk went down since baby started sleeping through the night.

I most of the time just give my baby breast milk, but my supply sometimes goes down so I have to give baby formula. How do you guys maintain your supply? My baby recently started sleeping 5 hours straight, then he wakes up every 2 hours until 9 am. I get really engorged and after I pump I only get 3 ounces from each breast. I ended up giving baby formula last night because he was hungry and wasn't getting any milk. I am so frustrated, sometimes I have so much that it hurts and I have to pump, and sometimes I am all dried out 😭. What am I doing wrong??