How do you know if you should try another formula?

Hi! I’ve been exclusively bf and pumping my 6 week old but I’m now finding I can’t pump enough and he’s refusing the breast. I’m supplementing with formula, but the first I tried (basic Enfamil) really bothered him to the point of being inconsolable for hours.

Now I’m trying the similac lactose free one and he’s still a bit fussy.. not as bad, but harder to get to sleep and crying a little more. He’s a gassy baby, we use gas drops and stuff as is. How do I know if this formula isn’t right? Should I wait a few days or try something else?

Thanks!!!