Missing a period can be caused by various factors, including pregnancy, hormonal imbalances, stress, changes in weight or exercise routine, and certain medical conditions. The pain in your left lower abdomen could be due to several reasons such as ovulation, ovarian cysts, pelvic inflammatory disease (PID), or even ectopic pregnancy. It is important to take a pregnancy test to rule out pregnancy as the cause of your missed period. If the test is negative and you continue to experience pain or other concerning symptoms, it is recommended to consult with a healthcare professional for further evaluation and diagnosis. They will be able to provide you with appropriate guidance and treatment options based on your specific situation.