my 2-mth old BB also suffered from no 便便 for 1 wk. i am also BF her, but having last feeding substitued by milk formula. i'd consulted a doctor before and she told me to put a themomether into the 肛門. Then the next day my BB had 便便. You can take it as a reference. Of course if your BB has accompanied with other symptoms, better consult a doctor.