Yay Hulk! He sounds like he's doing really well!!
They do grow fast - just wait! When we got Brodie on Christmas Eve (2 months and 4 days old), he weighed 10.4 pounds. Today, at his vet visit (4 months, 5 days old), he weighed 30 pounds!
And this was a dog with worms and digestive issues... Hulk may gain even faster, since he's healthier than Brodie was!