There are several possibilities. If you are sexually active and not on any contraception
is a possibility. Cramping in this situation could possibly be due to tubal contractions, but, the severity points to the possibility of tubal pregnancy. Another possible cause could be the rupture of an undiagnosed ovarian cyst
. Yet another option is some infection of the pelvis. Infections of the gut, appendicitis
and renal infections also should be excluded. The pain is usually relieved in ordinary situation with an anti-spasmodic. Hope this helps.