What are the odds I was pregnant, didn't know it and had a miscarriage?

[KryoAsteri]

So a little while back about three weeks ago, I got a bit worried I was pregnant cause my period came a little late about 4 day, but then it did happen but was really heavy and painful. Now I'm having random small spans of time would I'm bleeding a really dark brown color, with some random bad cramps and my left shoulder really hurts.

[OlderAndWiser]

You may have had an incomplete miscarriage. You need to consult your GYN.

[OddBeMe]

Do women get periods that nasty they can’t tell if it’s a fetus or not? Maybe don’t answer.

Body is a wonderland.

[dustybiker]

Please, call your doctor. Take care of of you.

[YAhallo]

How do you know you are pregnant?