Combining Enfamil AR with Enfamil Gentlease??

When we were transitioning from Enfamil Gentlease to AR we gradually decreased the old Gentlease with the AR until we are now on all AR.  But I've noticed that my baby appears way more cranky and is having trouble passing gas.  Not spitting up as much but is now super gassy.  Any advice???  Anyone ever heard of "forever" mixing two formulas in the same bottle?