Could be stress related. Also for girls who are underweight, they tend to have irregular periods or they could vanish all together.
ever body type is different some like that to . you will be fine if are still wording about it see a dr.
Hi there, hgreenway is right. Irregular periods when young are common. we can have a late period for a variety of reasons including stress, underweight/overweight/exercising too much, major changes in routine, illness, etc. Also, our hormones can have a blip that affects our period. Our thyroid can be slow (my issue at one time). Etc.
If your period doesn't show in the next couple of weeks, I would contact your doctor and try to be seen. You may need something to regulate you which is often birth control pills (they do more than just prevent pregnancy! )
good luck to you sweetie