How do i get my baby to latch on again?

I just had my baby a few days ago, i wanted to only breast feed, and he latched on pretty good, but due to his jaundice levels being a bit high, i had to supplement with formula to get that level down. My milk supply was also very good. Now he doesn't want to latch on, he'll just cry and cry and won't latch on. And my milk supply seems to be going down, even with pumping?