my baby is not gaining much weight😔

Hi fellow parents, My baby boy was born at 3.6 kg, now at 4 months he weighs 6.3 kgs.I am quite worried as he only gained 0.1 kgs for 3 weeks.last june 3, 6.2 sya and last june 22,6.3 kgs po m.Nagchange po kami ng milk from s26 to Nan HW kasi excessive yung pagsusuka nya sa s26.my baby anyways is a happy and active baby.only problem is the appetite and weight gain.any advice po?