Why will sometimes girls donot get periods?

Double check your bits. Even the most feminine looking of men will probably not get a period.

Stress, increased physical activity, new mwdications, new birth control. Could be anything. Don't freak out too much over it. If it really starts to concern you and hasn't showed ina couple of days, or a week, see a doctor.

Stress, weight loss, weight gain... there are lots of reasons. If it's just missing a period every now and then, it's probably nothing to worry about. If, however, you're past 20 and you've never had a period, then that is something to get checked out by a doctor.

Adolescent girls will need to reach a certain percentage of body fat (about 20-25%) before their period will start, so girls who are seriously underweight may never start menstruating.

Dieting and intensive exercise can be two causes. It used to happen with me.

Yes. Some girls can not get periods. If you are asking for yourself, I would like to suggest you to go to a doctor because it is a natural rule. And it means if something runs wrong, there will be some problems.
A girl without periods can have many problems. They can (I just say "can") not have children and other some diseases that makes they are weak, especially above 50.
I usually heard many old women around our house talk about their worry when their periods end soon pr late. Mostly, women who has their periods ended soon is usually face with flu..I don't want to make you worry. It is really necessary for you to examine now.

sudden and fast los of weight, too much sporting, but more often stress and bad diet....

Apart from one been pregnant, if not then it's definately have to be that culprit hormonal imbalance, I know that for sure.

Sometimes...they're pregnant...or hormonal imbalances....certain thyroid disorders....certain cancers.....stress...it could be a number of things. It's not unusual to miss one every now and then....if you're concerned...see your doctor.

I always miss mine when I'm super stressed.

There are a LOT of reasons for women to not get their periods. The most commonly known reason is that the are pregnant. HOWEVER, there are many other reasons and some are serious. Stress can also cause girls to miss their periods as well as hormonol imbalances, cysts on the ovaries, and cancers can cause menstration problems. If this person has had a normal period for a long time and this is the first time they have missed and they are not pregnant the should see a Dr. They should also see a Dr. if they are but you get what I mean hopefully. Best wishes.

anorexia, pregnancy, stress, side effect from the contraceptive pill. Get a check up to be sure.

Some just get it late, pregnancy, could go it but its really light so you dont notice it, being really underweight. Sometimes in rare cases you could be in menupause. But thats rare for someone young

If it is only occasionally, probably not to worry -- once a year. Otherwise, go to dr (not pediatrician!) and have blood tests done to check hormone imbalance and thyroid. Also for pregnancy, just in case. Many things could be cause -- too much weight loss or gain, too much exercise,stress. Please see dr soon!

i just got mine today! im 7