Random Period : Need help

Lakeisha
I've had my IUD since June and My last period was for an entire 4 weeks and I've been period free since July and loving it.  Randomly i started cramping and now I'm on my period, it's heavier than I remember and I'm convinced it may be an early miscarriage however if I take a preg. test now the results won't show. 
PS : after my boyfriend and I had some pretty intense rough sex I was literally in pain (cramps) could this have shifted my mirena or be the reason my period has started? Also I've been working out (running, light weights etc...)