Herbalist Susun Weed points out the difference between menopause which is the natural cessation of menstruation for women and amenorrhea which is lack of menstrual flow before the normal stage of menopause.
Amenorrhea is often caused by very low body fat which can be due to eating disorders, stress, or very intensive athletic training.
Susun suggests a homeopathic remedy, Ignatia or Natrum mur. Drinking nettle infusion regularly has been known to cause menstruation to recommence. A lack of body fat can be reversed with the addition of olive oil and butter to the diet.
Acupuncture treatments, or supplementing with vitamin E on a regular basis can help bring back ovulation and menstruation.
Dong quai root tincture along with peony root and licorice can cause the menstrual cycle to resume. This may not be recommended for those who tend to copious bleeding, or fibroids.
"Strong pennyroyal (Hedeoma pulegioides or Mentha pulegium) tea, a cupful/250 ml or more a day, for the three days of the new moon, can stimulate menstrual bleeding and restore regular cycling."
http://planetthrive.com/2010/07/amenorrhea