Aww, ang laki ng worry mo, pero okay lang yan! Sa mixed feeding, sometimes ang formula ay nag-cause ng slightly firmer poop compared sa purely breastfed babies, kaya hindi unusual what you're experiencing. But honestly, at 2 weeks pa lang, better check with your pedia para ma-assess properly, could be normal variation, or baka kailangan i-adjust ang feeding ratio or formula brand, kaya mas safe na marinig from your doc directly ang assessment niya.