What is the best formula milk?

Hello mommies. I just need help. Last month at my LO's 3rd month, 6.2kg ying timbag nya. S26 gold milk nya. But we noticed po na nagtatae cya evry after feeding. Tapos ni recommend nang pedia yung NAN lactose free. At his 4th month, 6.5kg yung timbang nya, bale 0.3kg lang ang dumagdag. Plano nami mag change nang milk for my LO. Ano kaya best na milk?