I dont have periods because of the depo shot and me and my boyfriend have unprotected intercourse. Latley I've been really tired and I have had lower back pains and what feel like twitches in my stomach.
It's common to stop having periods from the depo shot. Furthermore the shot is 99% effective against pregnancy if you have been getting it every 3 months as you should, so in other words you are very safe from getting pregnant.
Oh and you might want to research all the side effects from the depo shot. I personally would never use it, it's really dodgy.
Last time I read about those shots... it was an article of a woman that had died of blood clots in her brain (you have periods for a reason, and you shouldn't stop it).. If I was you.. I would consult a doctor. good luck.