Vomiting 19 day old help please

My son is 19 days old and today after most feeds will vomit/spit up what hes eaten then want more and do the same. its not all the time but only some days. He is burped but still is sick. I also keep him upright after meals for a while to try help it. Is this normal? i worry hes vomiting too much. He was born 8 pounds and yesterday weighed 9 pounds 2 ounces so weight gain isnt a problem. Any ideas of the cause? Or tips and advice? Thanks :)