Is this normal for a newborn?

Hi everyone. When my daughtr was born on Friday she weighed 6 lbs 15 oz. Today, when I went in for her first check up, she weighed in at 6 lbs 2.8 oz. And her bilirubin levels were elevated, around 15.9. Currently I'm using the phototherapy blanket at home, but I'm also concerned about her weight loss. They want me to supplement with formula every three hours, but she has been hard to wake up since we got home today and I've tried most techniques for waking up babies. She wakes up briefly then falls right back to sleep. Normal of a 3 day old? I'm not seeking any rude comments, but advice from other moms who may have experienced this themselves and how things turned out. I'm very concerned...how worried should I be? Thanks