Worried about my 3 day old newborn

I really need help as I'm a FTM and worried. My little girl is 3 days old and breastfed. She vomits after almost every feed, she even projectile vomits. I'm so scared she's ill or not getting enough. My milk supply is also already quite large. She can suck at the breast for ages or sometimes she'll only suck for 15-20 mins then be done. Can anyone shed some light?