Hi and thanks for the query, the commonest cause of failure to see periods in a female of reproductive age is pregnancy. Lack of periods warrant a pregnancy test first before looking for other secondary causes of missed periods of amenorrhoea. It could be interesting to know if its accompanied by bleeding or not. If not, a lesion of the ovaries, an ovarian cysts torsion of rupture i a possibility. Other causes of abdominal pain like urinary colics and infections must also be considered. An abdominal ultrasound a good clinical evaluation, preferably by a gynecologist is most appropriate. Thanks and hope this helps, Best regards, Luchuo, MD.