What Causes Frequent Periods After Miscarriage?

I had a miscarriage in Dec, 13th I didn't know I was pregnant so I don't how far along I was. After that I would come on every other week for about 5-7 day and it would b heavy. In March it came on the 25 th day and it was short. This month it was over a week late. I was on for 5 days. The day after my period I had a dark blood when I used the bathroom. P.s trying to conceive still...