My baby is 3weeks old and hasnt pooped for 3days.she is fully breastfeeding baby.any idea if its normal?

It is normal for breastfed babies to not poo for maximum of 14 days. Some babies poo everyday some babies poo once every week. You can cycle baby legs to stimulate bowel movement. If baby seems to have a hard time trying to poo, you can eat some prunes so that it can be passed on through breastmilk to aid them to poo.