It's impossible to guess what's going on. Dozens of medical conditions can cause a late/missed period. If you're not sexually active, have no reproductive organs or are in a same gender relationship pregnancy wouldn't be a concern and can be crossed off. Then you could look into other factors such as age, weight, medical conditions, etc etc.
how do you know your not pregnant? have you taken a test? i would advise you to see your DR find out y u have absent periods if your not pregnant. r u stressed this can stop your cycle big time?????????