Honestly it's normal. My son was breastfed and he too would occasionally have formula. Sometimes he would go a week without pooping. If you google it you'll see tons of articles about it being normal. Babies aren't constipated when they don't poop, they're constipated when they poop hard little pebbles. I definitely understand your frustration but try not to worry because honestly it's 100% normal :)
We did and they told me to massage his belly but I've been doing that and they said if that doesn't work then to stick a qtip in his bottom but they said it isn't hurting him so not to worry but I'm kinda worried @mrsruvalcaba