I've Been On Depo- Provera I Had My Last Shot

I've been on Depo- Provera i had my last shot on June 24th and I was due for my next shot on the 9th of September but I did not receive my next shot. I had sex on the 13th and on 14th I had some light spotting. I still have been sexually active since then. Also I've been experiencing nausea breast tenderness and back pain and some mild cramping. What are the chances of me being pregnant