Just curious

Amarisa • VT Original. 802. I am who I am. And sometimes even I don't like me.
So I am almost 22 and I've been on the Depo Prevera shot for I want to say 7 years or so. Since I was 16 at least. I know after a while your body can build up an intolerance to certain things. With that being said what's the possibly of getting pregnant while your on birth control?