He might he eating too fast? Is he bottle fed or do you nurse? Try burping him half way through the feedings, it should help some. If you bottle feed maybe try switching brand of bottles. If he seems really fussy, maybe ask your ped about him having GERD?
It could also be pyloric stenosis, which usually kicks in at about the 3/4 week mark. It is recommended to see your doctor if infant projectile vomits after three consecutive feedings or I have read even if just once a day.
My DS did it a couple of times. As mentioned, trying to slow down the feeding, stopping to burp during, and keeping infant in upright position helped a lot.
Research acid reflux. Sometimes the symptoms come as they get older so they could just be starting. Important to talk to your ped and go over symptoms though. Our neighbor's little boy could not keep anything down and they ended up having to operate on him. Not trying to scare you! Just saying it's important to address the issue.
Re: 1 month old baby vomiting
My DS did it a couple of times. As mentioned, trying to slow down the feeding, stopping to burp during, and keeping infant in upright position helped a lot.