What Causes Spotting Between Cycle After Undergoing D&C For Fetal Demise?

I had a d&c after 15 week gestation fetal demise. Cycles have been 28 days, then 28 days, then 23 days and this last one was extremely heavy. I have noticed I spot mid cycle usually on day 12-14. I am confused. Am I ovulating? I have been using the opk and bbt. The day after the bleeding my temperature rose. Cannot seem to get a positive opk.