Mid cycle spotting...

I had a miscarriage in July. My period last month was light and only lasted 3 days. And yes I took a pregnancy test and it was negative. Normally my periods are heavy at first and last about 6 days... I got a positive ovulation test last thursday. Yesterday I started cramping a little and spotting. And this morning I'm spotting a little also... I have no idea why. I've never had mid cycle bleeding before. Anyone know what this could be?