Ethan's gut

Ethan's not been eating much and he pukes more often?? that's the impression my mum and I have. Poor thing has lost weight. He eats now about 300+ml of milk a day and only about 100ml per time, sometimes less. That's not normal for a 6 month old right? Doesn't seem to digest the weee bit of semi solids we stick him. anyone out there knows if there's a problem?