For almost a year straight I ve started my period on the 16th of each month and lasts for 5 days (since my very first period it s usually been 5 days long). In February it came on the 19th and lasted 6 days, March it came on the 23rd and lasted 5 days, April on the 21st and lasted 4 days. I downloaded an app and it says I should have gotten my period on the 16th of this month. Is this considered irregular ? Is this normal for my period to fluctuate like this?