What is wrong if you haven't started your time of year contained by 3 weeks and you haven't have sex?
Answers: Stress can make you miss your time, you could end up being in arrears, or miss a month even 2 or 3 months completely because of it. Other causes that can lead to missing it is focal change in diet, and exercise also. Or it could be something serious, but i doubt that single missing a month would be serious, now if she was getting a abnormal discharge, or not getting her period for months on end, that would be something to jump to the doctor about..
depends on how old your friend is, and how much she weights. Has she changed her diet/lifestyle not long? is she on any medications, as this could actually be a side-effect of something. have she had such problems in times gone by? does she have any other symptoms?
you need to mention more info. it is impossible to relate otherwise!! well depending on her age...she may just be for a moment irregular. i know teenage girls between 14-17 are sometimes dramtically irregular. if she hasnt had sex...in attendance really isn't anything to worry about. if she is still vastly worried make a drs appointment is all i can voice..
It could be that she is stressed and that can sometimes make your period behind. Maybe she has a longer cycle than everyone else, everyone is different in the time between period, I am 33 days between! I wouldn't worry for another week or two yet and after go see your doctor! all the best.