What Causes Severe Pain In Chest And Abdomen While On Depo Shot?

I have been having unprotected sex recently. I was on the Depo shot, I was supposed to go back for my second shot on July 8th, I didn't. And now I have been having lower back pain and stinging kind of sharp pains in my chest and stomach area. A few weeks ago I was very tired all the time and had a heighten sense of smell and taste. Since then that has stopped. I got my period july 13th so I am do next week. Could this be signs of pregnancy if so when should I test to get an accurate result.