My 6 wk old has not pooped in 4 days. i'm starting to get concerned. when does it become a problem and she needs to go to the dr? breast fed

Probably OK: It is not unusual for a breastfed baby to have infrequent stools starting around one month. Think of it this way, human breastmilk is the "perfect food" for a human baby, right? There is less "waste" therefore to be "pooped out" so to speak. As long as she is not having a distended, swollen belly, or the stools she is having are hard and painful to pass, this is fine.