Eh, sudden change macam tu memang boleh jadi tanda ada sesuatu, bisa formula nda suit, atau ada gastro infection ke apa, better check with your pediatrician cepat-cepat sebab baby kecil lagi. A few of my mum friends had similar situation with their babies, and ternyata some babies memang sensitive to certain formula brands, but ada jugak yang kena mild infection, so kena jumpa doctor la to be safe.