Aiyo mommy, 6 days no poo is quite long lah, even if baby seems happy and perut tak kembung, better to call your pediatrician or clinic just to check, especially since you're mixing BF with formula, as sometimes it affects their routine. A few of us tried waiting it out thinking it's normal, but our doctors said better safe than sorry, so ring them up lah, they can check baby's tummy and put your mind at ease!