Im not the type of person that calendar's my periods, I'm a regular kind of person who has one within this one week a month.

I am per menopause and there has been a time I have had a period twice in one month and nothing the next month, but when things went to normal it was back to that week.

I believe that meds can mess you up, but your talking a few days. Some months are longer as well.

Just my two cents.