Sometimes it is usual for a mild diarrhea
to occur just before the onset of a period due to the prostaglandin
release that happens prior to the onset of menstruation
. As you have been having this pain and sickness, it is more likely that you have an infection and need to be treated. You may see your doctor for an exam and if you miss your period, you can wait for a couple of days before taking the test. You may need medication for your gastro-intestinal ailment. Take care.