Period and breastfeeding

How long after stopping breastfeeding did your period come back? I stopped 6 weeks ago and still haven’t had my period. My son is 7 months old and I was only pumping 2 bottle a day so I’m surprised it hasn’t come back yet... and I know this may sound dumb but has anyone fallen pregnant without getting a period first?? I’m not on any birth control and I’ve taken 2 tests but they were both negative...