In general, nausea and vomiting rarely occur before menstruation, if nausea and vomiting may be related to the following reasons: 1, poor gastrointestinal function, coinciding with the premenstrual period, may also be caused by hormonal fluctuations. You can observe conservatively, you can also take stomach and appetite tablets, as well as a light diet to improve, if after menstruation still no improvement, go to the hospital for examination. 2, liver abnormalities, if suffering from viral hepatitis, will appear nausea, vomiting, aversion to grease and fatigue symptoms, and even jaundice, to isolate early. 3, early pregnancy, early pregnancy reaction occurs in about 40 days of pregnancy, because there are individual differences, early pregnancy It is recommended to take blood test for HCG level, if HCG is more than 10mIU/mL, it is clear that you are pregnant.