Aw, yan talaga ang challenge around 18 months, ang milk supply naturally drops kasi ang babies start eating more solids, pero ang picky eaters ay ayaw talaga ng formula! Have you tried mixing your breastmilk with the formula first, or even mixing different brands together to change the taste gradually? A few of us did that trick and it worked, plus you're still giving them your milk kaya may nutrients pa rin. But honestly, if you're concerned about the supply drop or kung kumakain siya ng enough overall, better check with your pediatrician para sure, they can guide you on what's normal at this age and if kailangan pa ng supplements. In the meantime, keep breastfeeding on demand pa rin kaya the more milk kailangan niya, the more your body will try to produce.