Secondary amenorrhea is the lack of menses during the menstrual cycle for at least 3 months  at any time after menarche of the reproductive female.
The causes of secondary amenorrhea can be hormonal or uterine.
Hormonal anovulation can be caused by pregnancy, hypothyroidism, hyperprolactinemia, hypothalmic factors (potentially caused by brain tumours), polycystic ovarian syndrome, malnutrition or late onset congenital hyperplasia.
Uterine amenorrhea can be caused by endometrial failure, such as in Asherman's Syndrome.
A thorough history should be taken that includes menstrual history, pubertal milestones, sexual history, contraceptive use, a history of pregnancies, and a functional inquiry.
Tests should also be run, including a βHCG, Progestin with or without progestin & estrogen, TSH, FSH, LH, prolactin, and potentially radiological Investigation.