So I'm 21 years old and I have a twin sister and I also have a 23 year old sister. All of our periods are so irregular. I'm pretty sure my older sister gets her period about once a year and my twin sister got hers 3 times this year. Where I've had mine in August of last year (2016) and didn't get it again until March (2017) and then I had it from June 13th- July 18th (and it was a full blown period, no easy days at all) and then got it again in August for around 4 days and finally I had it from December 12th- 14th. I seriously have no clue what's going on. I know irregular periods aren't necessarily normal but is it weird that all of our periods are like this?