Increase fm intake

Hi mummies, wondering how to know when can increase my baby fm intake? Worrying abt underfeeding & overfeeding my 8 WEEKS LO. Trying increasing little but her feeding intake not consistent, sometimes she can finish the milk( if not showing not enough)but sometimes she can’t finish the milk & will doze off halfway thru..#firstbaby #advicepls on another note, does any mummies try mixing little bb cereal into fm to make lo feel full? How old advisable to do that?