it is normal i wondered the same thing but i talked to many doc and gyno since then and its normal and period can be compleatly unpredictable depending on individual person the perioud can last a whole month sometimes and can happen 2 times a month with a pause but im on the birthcontroll shot that lasts 3 months so i dont need to worry about it anymore for the most part i still get a short one at the end of the 3rd month but its way better than every month sometimes 2 times
go to your Dr they will probably put you on birth control pills if you aren't alreay to regulate your period