[Age of Ignorance]

I guess you'd know for sure if you took a pregnancy test, but even that's not a guaranteed answer.

From my understanding of the depo-injection, an egg is not released from the ovaries. Basically, for three months, you might get some light periods (or even none), but the egg will still not have been released. Over those three months, it's almost assured that you're not going to fall pregnant, regardless of whether or not you have a period. Because of the lack of menstrual bleeding, it is of course difficult to tell whether or not you are pregnant, but the odds of being pregnant are extremely slim. If you are pregnant and on the depo-injection, you shouldn't know unless you start exhibiting other symptoms related to pregnancy. If you do have other symptoms, then you should take a pregnancy test. Otherwise, you don't have to worry about it - a lack of period is a side-effect of the drug, and you shouldn't base the possibility of pregnancy on that.