On depo, next shot 1/30/15. why am i having bleeding/spotting and lower back pain ?

Unstable lining: As you get close to the next dose, the lining may be a little unstable and bleed. It does not effect the birth control aspect of the Depo, you are still protected.

Normal depo effect: Irregular periods are the norm on depoprovera. Many patients have no periods at all. Others will experience irregular menstrual bleeding. This is how Depo-Provera works. If you are not satisfied with the bleeding pattern on Depo-Provera then consider using a different birth control method.