I'm not experienced and only have book smarts. But from what I understand formula is a lot more filling than breastmilk and should last longer. Had you tried increasing the amount during scheduled feeding, or is your baby burping out a lot of the milk he drank? Also had you checked the powder/water proportions are correct? There's a chance he may not be hungry too, had you tried distracting him with a pacifier or interaction? Hope some of these suggestions help and good luck!