Question on formulas

I am a FTM. I had my son last November. He is almost 5 months now. He has been on Enfamil gentlease since he was a few days old. He was getting breastmilk as well but the majority formula. (I was an under producer as well as other issues I couldn't breastfeed but I did pump what I could.) My son has never had an issue with the gentlease. All of a sudden the past month/ month and a half he started spitting up a lot. He is going through several outfits a day at daycare. He is still drinking breastmilk everyday as well but it is so minimal it shouldn't effect him every bottle. He only gets maybe an oz a day of breastmilk. This past weekend I bought a can of the Enfamil AR so we could try it and see how he does. He absolutely hates it. My son is not a fussy baby either. I told my SO Saturday to try mixing the 2 formulas together and see what happens. 2 scoops of the gentlease and 1 scoop of the AR. This is the 4th day and he is not spitting up like he was and he eats it all.

My question is should I just continue to do what works or should I try to completely switch him over to the AR even though he hates it and refuses to drink it?? Has any other mom had to mix 2 different formulas? I'm just seeking advice or opinions because I want whats best for my son.