Periods after postpartum different than pre-pregnancy?

Not sure this is the right category for this question, but I'm not TTC. I'm 21 months PP and my period returned around 14 months PP. The quality, let's say, of my flow is much different than it was before I got pregnant (it didn't change after my first miscarriage; second pregnancy went full term and gave me my darling son). It's not nearly as robust as it was before; it's so scant I don't need a pad the entire duration, and it's a much darker brown than bright red. Pretty much just like spotting the whole time. My ND knows about the change and recommended some things to get it back to a healthier state, but it's not changing over the months. I'll also add that I have, or had before getting pregnant, PCOS.