Mixing formulas?

Tiffany
Just curious if anyone has tried mixing enfamil gentlease and enfamil AR. My son is highly gassy and fussy, but recently he has started spitting up a significant amount of his meals he's on gentlease now I was thinking of adding enfamil AR. His pediatrician has no thought on the matter, she says spit up is perfectly normal, I just feel his amount isn't.