A detailed evaluation is necessary for correct diagnosis and management of your problem. Few common causes of lower abdominal pain are PIDs, ovarian cysts, fibroids, STIs, RTIs etc. Scanty menses can be seen at extremes of reproductive life like just after puberty or before menopause. Stress and anxiety suppress the activity of the centers in the brain that stimulate the ovaries resulting in low production of hormones and hypomenorrhea.Tubal adhesions ,PCOD,uterine hyoplasia,excessive exercise and crash dieting all can cause scanty menstrual periods .You need to seek medical help. Investigations like hormone levels, ultrasound pelvis may be needed to determine the cause. Do keep me posted.
Best of luck and regards!