I've mentioned it before on this site, and I'll do so again, because it's funny and describes lochia well... postpartum bleeding is also referred to as "the mother of all periods". It can last up to six weeks, and is unlikely to stop before two weeks postpartum. Lochia cleans the uterus of all remaining tissue, but it does not mark the start of regular menstrual cycles. Breastfeeding can keep those (horrible, right?) cycles away for a lot longer, but not always. I was lucky to go without menstruating for 21 months after the birth of my youngest child, but also have friends whose periods started months after giving birth. By the same token, bottle feeding mothers can also win the menstrual lottery sometimes, but they probably will not get to 21 months.
You might have a few anovulatory periods when your cycle does start up again, but it is difficult to know the difference unless you use ovulation tests. Many women who had painful periods report that menstruating is, literally, less of a pain after they became mothers. Others say that their periods actually became heavier and in some cases more crampy. The same "non rule" goes for the regularity of cycles; some moms get regular cycles like before, some women who previously had irregular periods stay that way, and others switch around. When it comes to postpartum periods, expect the unexpected... and (yes! another stupid pun!) go with the flow.