Hi and thanks for the query,
the commonest cause fo missed periods in a female of reproductive age is pregnancy
. Its interesting to know whether this test was actually reliable and could be worth repeating. I suggest you visit your gynecologist for review. I think an abdominal ultrasound
is very important to do, and maybe a blood BHCG test, which is most effective to either diagnose or exclude pregnancy, diagnose extra uterine pregnancy, ovarian cysts and other causes of bleeding. Its however, not unusual for female to have anovulatory cycles with cycles with mild staining of blood, but with no actual pregnancies.
I strongly suggest you visit your gynecologist or start with the emergency room.
Thanks and best regards,