Spitting up & slow gainer

Just got my sons 2 month shots and when they checked his weight he was in the 1 percentile 😞. He eats really good but than spits up a lot like a lot it’s crazy. He’s a happy healthy baby so I don’t understand.

Anyone have this happen? He was 6lbs 7oz at birth and at 8 weeks 9lbs 10oz.