What Causes Spotting And Heavy Periods After Miscarriage?

I had a miscarriage last yr in July, got the depo shot soon after and never went back for the next one. I got my period back in October 3 months after the MC, they have been really heavy since then, I was supposed to get my period on the 9 of this month but never, yesterday I had brownish spotting the went away, today I have pink spotting but not enough for a pad. All of my periods start off heavy never with spotting, and with my other two pregnancies I never spotted.



What could be the problem?