Mixed Feeding

Hello, mommies. I'm a first time mom to a 2 (almost 3) week old baby boy. Hindi enough ang milk supply ko even though I'm doing everything I can para ma-increase sya (consume masasabaw na food, take Mega Malunggay, drink Milo, drink lots of water). So what I do is binibigyan ko rin ng formula milk si baby (S26 Gold). How can I make sure po that I'm not overfeeding him? We feed him formula milk every 3-4 hours. Then throughout the day, I breastfeed him too kahit hindi ako sure kung may nakukuha ba talaga sya. I'm worried he might be overfed— how can we avoid it po ba?