Do Nausea And Lethargy After Missing Depo Shot Indicate Pregnancy?

I think I might be pregnant. My last depo shot was in july 2014 I was due at the end of September 2014 for my next dose. My dr retired and didnt inform anybody so I couldn t get the shot. I was haveing sex but my bf would pull out and nothing would happen but on new years eve/early newyears morning we had sex and he didnt pull out so he ejaculated inside me and that morning I had a lil bit of blood and it stopped then it got really heavy and now its the 4th and im still bleeding. Last night I couldnt sleep cus my back hurt and it was so uncomfortable. And today im naucious and really tired. could I possibly be pregnant?