Baby losing weight

Hi my baby is around 11 months now. He became very active, really active and tends to have difficulty sleeping at night. He will go rolling, playing tirelessly until he falls asleep in weird uncomfy position. He also had reduced appetite eating and drinking his milk. Sometimes he throws up all what he ate/drink if he feels full. He is not a chubby/plump baby to begin with and has a light slim body. We worry that if this still continues and he starts walking already then his weight will really drop some more. Only thing that lessen our worry is that he is not getting sick frequently. Is this normal for this age?