6 weeks like clockwork for me x 4
With #1 we had bf problems so she was getting formula and I was pumping and bf'ing part-time and gave up by 2-3 months. Got 1st pp period at 6 weeks.
With #2, #3, and #4, very successful bf'ing, nursing round the clock, etc. #2 had no soother but my boob, #3 did take a paci, and #4 found his thumb early on (which still amazes me--never had one express even a mild interest in their thumb before)--but none of them slept more than 1-2 hours that early on. All of those--1st ppp at 6 weeks. And yes, fertility too--#2 and #3 are 13.5 months apart--you do the math.
Guess it's just how my body works.