Hi,
Over time you might notice that your period will occur on different days of the month; it might be a bit earlier than you expected, or a bit later than you counted on. That's 'normal' for a lot of us. The length of your menstrual cycle can change from month to month for many different reasons, for example: if you are stressed about anything; changes in hormone levels; dietary changes; have experienced an illness recently; changes in medication or birth control, and so on... The average menstrual cycle is supposedly 28 days long (from the 1st day of your last period, to the 1st day of your next period), but often that's not typical for every woman. For many women, slight changes in menstrual cycles are normal and are something we come to accept. Once your period changes it will usually move up, or can decrease, the next expected calendar dates of future periods. I hope this helped ease some of your concerns, take care :)