Contraceptive hormones can be a cause of absent menses. Weight changes, changes in exercise pattern, travel accross time zones
, and stress (new home, new job) can all contribute to "secondary amenorrhea" (cessation of menstrual flow). Hormonal issues include thyroid disorders, prolactin disorders, and androgen disorders.
If menses are absent for 3 months and pregnancy test is negative, a test of the hormone environment with progesterone or Provera is the usual next step.