New moms help with feeding question

My baby is 5 days old and lost 10 ounces. I am trying to get him to latch but it’s tough so I pump but get two tablespoons after 15-20 minutes so I am forced to supplement with formula an ounce or so per feeding since his bilirubin is high and he needs to poop it out. Any advice? How do new moms know baby is getting enough from th breast? I really want to breastfeed. Thanks.