NEED HELP!!!! 😪😭

So my little one is 3 weeks and I thought I was producing fine as of my baby's 2 week appointment I was strictly breastfeed him but he lost 1 pound and was severely jaundiced. So my LO Dr. told me to supplement with formula but also pump afterward but as when I pump I only get a 1oz both boobs. I put him at breast first but he sucks me dry and he with be at breast as long as he want until he get fussy then I supplement him. But my question is how can I get my supply up!! I have Pcos so I'm not sure if that's has something to do with it. Also with my two other children I had the same problem but I stopped with them. But with my baby boy I wanna breastfeed still 1 but i wanna be able to give him enough so I don't have to supplement anymore.