How much has your baby gained since birth?

Ash • Married 8.2.2014. 1st Boy 11.24.16. 2nd Boy 8.27.18
My son was 8lbs 2 oz 21.5in long. Now he's over 12lbs and 23in long at 6 weeks! He's breastfed only. He doesn't have a lot of rolls or anything though. His Dr isn't concerned, said it's great, but people have made comments about how fast he's grown. My gyno was shocked at my 6 week check up. So I'm a little nervous. What's everyone else's babies at?