no period not pregnant

i haven’t had my period yet and i’m 5 days late according to eve, i’ve taken 3 pregnancy tests in a matter of 5 days and they were all negative. i usually start cramping and my boobs get sore the day before i have my period but i haven’t had any symptoms!! anyone have any explanations? i’m not on any medication or anything and i’m 5 months postpartum but i got my period at 1.5 months PP and it’s been regular ever since. (not on BC either, we use condoms and he pulls out as well)