According to LAM guidelines, if you are practicing ecological breastfeeding, any bleed within the first 56 days can be ignored. But you have to be meeting the seven guidelines for ecological breastfeeding. http://www.nfpandmore.org/The%20Seven%20Standards%20Summary.pdf
With my first two, I started cycling regularly at 6 weeks and 5 weeks pp. With the first one, I had a pp infection and was told I could not breastfeed on the antibiotics I was given. So he received bottles and I pumped and dumped for 10 days. With my second, she slept through the night very early on. After those two, my next baby I enjoyed 5 months period free, and from then on I was tandem nursing my toddler and newborns, and have experienced a year or more of infertility.
I am on a email listserv with Sheila Kippley and she says that women that do not experience a lengthy pause in fertility while breastfeeding almost always are failing to take a nursing nap with the baby. It gets harder and harder to do with older children, but that is what she has seen in her many years of experience.