I also seem to have had a disappearing AF as seemed to have one around 6 weeks, then occasional little bleeds which last no more than a couple of days. DD is now 13 wks and thought as she is now sleeping through the night i would be landed with regular periods (happened with ds about 6-8wks then normal periods). So am feeling strangely relieved that they seem to have disappeared again.
Apparently having a period at around 6-8 weeks is completely normal and is part of the lochia, sort of like the withdrawal bleeds you get when on the pill, ie an effect of the pregnancy hormones leaving your system. But it's just a one off thing.
Then if you are breastfeeding you often don't get another one until feeds start to drop off a bit - was 18 months for me, but it varies
SImilar issues here, even though I am only expressing, 3 times a day. Ds is 16 weeks and had af at 4 weeks, 6 weeks and 8 weeks, then it went awol for 7 weeks and when it did appear was really light, not what I was used to, but having poas 3 times with a -'ve I think it probably takes a while for our bodies to adjust. Fingers crossed af continues under it's new guise!