Irregular periods

I was on the depo for a year took my last shot in September been trying to concieve since. I've heard that some people didn't get a period until a year after being off. I got mine a month after I got off. I've noticed that my periods are getting closer together.  I'll have one at the beginning of the month and then I'll have one at the very end going into the next month. I'm suppose to start in 5 days which seems too soon. Does this mean the shot is out of my system? I don't feel like I'm going to start I normally get those weird stomach cramps. Has this happen to anyone?