How can I tell if my baby is getting enough breast milk, since I can't count the number of ounces?

Feed on demand. Babies are smart enough to know when they are full and bcoz they have small tummies plus breastmilk is faster to digest than formula milk, it's common if baby wakes up every 1 to 2 hours crying for milk. Just monitor his wet diapers accordingly to ensure that he isn't dehydrated.