I think I agree with previous post,if you were 2 weeks late,then a test would have been positive,some months our periods can be bad.as for being late,chances are you ovulated later,maybe due to illness or stress maybe.I would say its just a nasty period.if your concerned in any way,contact your doc,as if it is a mc you want to make sure there is no infection.
My periods were always very clotty started off lightly then got worse so it could be the same in your respect. When i had my two miscarriages i also had some quote painful cramping as your womb contracts as it passes through the baby not nice but i would say if you have had a miscarraige then you would know about it.