Weird periods

The past two periods I've had, there's only been blood, no tissue at all. I'm just wondering if this is normal or something I should talk to my doctor about. I had a miscarriage about 5 months ago. I went to the doctor shortly after, they examined me and said everything was fine. Of course I experienced some irregular periods after that but this is just weird. I feel like the miscarriage was too long ago to be causing this but I don't know. Anyone have any explanations?