I have my twins on Similac Sensitive. They’ve been on it for almost 2 weeks but still constantly grunt arch their back and stay fussy. I use dr. Brown bottles and they’re going to be a month old but were born at 35+6. I’m a first time mom so I’d hate to switch formulas on them if it’s just a newborn/preemie thing. Their 40 week due date is this coming Monday. They are full of gas constantly no matter what I do. I’ve tried gripe water and simethicone drops. Are my boys just gassy or do they need a different brand of formula?