Ay, switching formulas is always stressful kasi takot tayo di aadjust ang baby! Honestly, marami sa circle ko ang nag-switch to Similac at okay naman, pero parang mabagal talaga ang weight gain sa ilan depende sa baby, every baby is different talaga, plus it takes a few weeks para makita ang changes kaya huwag masyadong mag-worry ngayon pa lang. Since baby mo naman ayaw na ng NAN and you're concerned about the weight, maybe check with your pedi para sure na okay lang ang growth, at they might recommend kung kailangan pa ng adjustment sa feeding schedule or formula mix, just to be safe!