6 week old projectile vomiting

He son is 6 weeks old and for the last week and a half my son has been projectile vomiting at least once a day the last couple of days it’s been more like 2 or 3 times a day. he went to the doctors and they said he looked normal but it’s still happening and getting more frequent. He’s gaining weight and is a pretty happy baby most the time. We’re really worried about him. He is breast feed and it happens when he’s eating up to 30 mins after he eats. It looks like straight up milk like it’s thin and not chunky like spit up.

Anyone have this happen or know what could be causing it?