Why did this happened?
Why have my menstrual been on for 7 days? I have a 5 day period. For some reason it Change. What happened? HELP.
It's normal to change. If you're really worried about it though, you could always visit your gynecologist.
If you are just getting into your teenage years this is normal as your body is acclimatizing to the changes taking place within it. Pregnancy is also another cause of irregular menstrual cycles. You can read more on this at http://women.webmd.com/tc/missed-or-irregular-periods-topic-overview.