2 months old Baby’s weight

I was told by polyclinic during the usual development checkup at approx 2nd month of my baby that his weight has went up pretty drastic despite him was given birth smaller than average. At 2month plus he has gained about 3.4kg since birth, I’m wondering if any mom has this issue and that is it something common or I should be super worried about? #pleasehelp #firstbaby