Period missing for nine days left sided pain beneath chest and to the back pregnancy test negative?

Missed period: Missed period is not just caused by pregnancy, although, pregnancy is the most common cause of missed period in women of fertile age. A lot of women fail to ovulate and that causes them not to have a period that month. They either get it back next month or they go without one for a while until they start bleeding uncontrollably when the uterus line grows big enough to just slough off on its own.