baby vomiting

Rachel
My baby's last feeding was at 11:00pm and he vomited at around 2:30am while he was sleeping. Now it's 5:30am and all he's eaten is an ounce of breastmilk. He's been fighting a stomach bug the past few days. I really don't know what to do .. should I let him sleep without eating more? He usually says 3.5 oz.