I had the depo shot in June and had light spotting for a week at the end of July. I had no period until the end of November and it was regular. A week and a half after that I started spotting again - brown, red, pink with the clear mucous discharge. I was heavy for one of those days and it lasted a week. I am two weeks late for my scheduled period and I have had sore nipples for eight days, and now lower back pain. I took 4 HPT and they were negative. Could I be pregnant?

The shot plus all the side affects make it hard to tell. Have you had intercourse anytime before or after the depo shot? Sometimes when pregnant before the shot it may show up as a false negative due to the vaccination. I would wait at least a week before taking another pregnancy test. But some of the side affects you are describing sure sound like a pregnancy.