Newborn vomiting?

I have a 2 week old son who was born 3 1/2 weeks early.. He has been vomiting after he eats.. It's not til like an hour after he is done and its not everytime.. He vomited once in his sleep and once projectile.. Its not your normal baby spit up.. He also chokes between feedings.. I am feeding.. Has anyone had the same thing? Should I worry?