Could Heavy Bleeding With Grey Clots After A Late Period And Negative Pregnancy Tests Be A Miscarriage?

My period was around a week late. I took two pregnancy tests in that time and both came back negative. I then started to light bleed which could of been mistaken for spotting. This morning I woke up with bad stomach pain and heavy bleeding. I have since passed two grey clots covered in blood. Could I be suffering a miscarriage