How do I get a good milk supply?

Jessica • 12/13/16! Kaylee Elizabeth wolfe,Charles James 1/10/19!

I am 4 days pp and my milk still hasn’t come in. I have been feeding my baby and I also have to supplement with formula since he lost over 8% of his body weight and is almost jaundice. I always put him on my breast first until he starts crying because he doesn’t get enough milk. Is there anything else I can do to help get my supply up