Hi and thanks for the question, the commonest cause of absence of periods or amenorrheoa in females of reproductive age is a pregnancy. If you have had at risk sexual intercourse within the period, it shall be worth doing a pregnancy. This shall be important in eliminating other differential diagnosis like an ectopic pregnancy. Brown vaginal discharge on its own could be some rare menses, which i common in females of your age, or as you describe, due may be fowl smelling nature might need further investigations. A vaginal swab with direct microscopy, culture and sensitivity tests shall be important in diagnosis given causative agents and possible antibiotics that might eliminate them. Right lower abdominal pain could arise from gynecologic as well as non gynecologic causes. An ectopic pregnancy, ruptured ovarian cyst or appendicitis are commonly found diseases that need to be eliminated in the firs place. Doing an abdominal ultrasound shall be a key tools to put things together. I suggest you book an appointment with the gynecologist for a proper evaluation, clarification and drawing up of an appropriate and adequate management plan. Avoiding unprotected sex during this period, if you are sexually active, could be crucial in preventing sexually transmitted infections, in case found to be transmitted to or from a partner. Couple consultations in such cases might be the ideal situation. Thanks as I wish you the best of health, Luchuo, MD.