On Depo-Provera provera (medroxyprogesterone) for 14 months and no period since day one. I started cramping/spotting 3 weeks ago after intercourse. No stds. What could be the cause?

Stop and check. Most women can use depo-provera. However, it is not recommended for women who have: unexplained vaginal bleeding liver disease breast cancer blood clots. So please see a gyn before start again...