What Causes Vomiting In An Infant After Drinking Milk?

My son is 10 months old and I just recently changed him from formula to milk. Ever since he throws up what looks like cottage cheese. He does not do it every time but it s very often. He was on Nutramigen until 6 months of age and from 6 months to 10 months on gentlease so I figured he was over his milk protein allergy. Could he still have an allergy towards milk and that s why this is happening?