Depo and chances of being pregnant...or something else?

Ok so I've been on and off depo since I was 15 (23 now) and this is the worst episode I've ever had. So in Sept. I was bleeding from the 3rd until the beginning of Oct. So I'm back to having again and since the bleeding has stopped every time me and my bf have , I cramp, and the cramps r bad... like contractions almost. Sometimes its focused on my left side, sometimes its dead center. So we did it last night and during it seemed like stuff was movin around. And now today, im cramping like crazy back pains and I its down into my legs....what the heck is goin on??