My lower abdomen hurts on the left side. How do I know if they are menstrual cramps or something serious like appendix?

Appendix is on. right side. Left side pain could be menstrual cramps, or could be ovatian cyst, ectopic (tubal) pregnancy, divefticulitis, ureteral stone, other; tumors/cancers possible, but less likely. Got fever, vomiting, change in weignt, bowel habit, bleeding, change from usual menstrual symptoms, etc, needs MD ASAP. At all different from usual, see MD.