What Causes Back Pain And Bleeding While On A Depo Shot?

hi i m 16 years old and I am sexually active with my boyfriend. I am on the depo shot and have been for 2 months now and my next shot is due in june but lately I ve been having lower back cramps and bleeding a really dark color with blood clots. I m concerned weather I am pregnant, also today my boyfriend and I decided to smoke weed and began to have sex. afterward I stood up and my vision began to blur and everything began to get black. I felt week, my ears were burning, I began to get really hot, and my breathing was short and fast. I started feeling better but I still felt dizzy and sick to my stomach. Am I pregnant if not what happened and am I going to be okay?