Talk to Gynecologist on Flat Nipples

I had delivered my baby 5 days before through c sec. He was on formula fed through spoon for two days. Now he is not latching my breast and gets frustrated and starts crying. I end up giving him formula I pump manually to pop my nipple but it is of no use. I am so much worried and depressed. What should i do so that he starts sucking it and my supply doesn't get lower