How can i help my 3 week old poop? i breastfeed, and hasn't pooped since yesterday evening.

Don't help, he's ok: Not all babies poop every time you breastfeed, in fact, the normal range for a stooling interval is anywhere from a few hrs, to weekly!! Try not to fixate on how long it's been since the last poop, rather give it a few days, and if nothing is happening, a tsp or 2 of Karo corn syrup in the bottle should loosen up the stool to allow regular pooping.