When did u know if was time to change formula

What kind of formula do you use? And if you don't mind me asking why are you wanting to change it?

When he started spitting up too much and getting bad gas. I changed to gentle formula. Not soy though.

It's the blue one I need answers bad he is lot of pain

I don't want to change his formula it's just he is in pain stomach pain every time I finish feeding him and during the feeding it's so sad