First off, you never said if you were late for your period. What signs of pregnancy were you having? Pregnancy signs and PMS signs are very similar.
How late was your period? A missed or late period can also cause extreme cramping and clotting. A lot of early miscarriage don't, by the way.
No one on a message board can tell you whether you are having a miscarriage, have had a miscarriage or were ever pregnant or not. You will need to take a pregnancy test - there would be enough hormone left in your body for a positive if you are or were pregnant.
Do not take this lightly. A miscarriage can cause severe bleeding if that is what it is. You will need to be seen by a doctor!