my periods keeps fluctuating 25 -28 day every month , some months on the 25th day, some months on the 26th day,others 27 and 28th. last month my period came on the 8/10/13 and i ovulated on the 8/23/13,i ve been for cramping since 9/4 and period is not as of 9/6/13. is this normal with the fluctuation and everything?