why is my period late?

1. A Change In Your Regular Routine: Change your wakeup time? Go on vacation? It can take your body a little time to adjust to a change in your regular routine and that can impact your regular cycle, especially if the change started at the time you would normally ovulate, causing a delay or even a skipped cycle.

2. Stress: Your emotions, particularly stress, can have a major impact on the regularity of your menstrual cycle. And if you’re stressing about why your period is late, that could actually delay its arrival even more. Mother Nature is a cruel mistress!

3. Illness: Being sick at the time you normally would ovulate can delay ovulation — and if you ovulate late, you’ll get your period late. So if your period hasn’t arrived on schedule, think back a few weeks — were you under the weather?

4. Pill Poppin’: Taking a new medication or changing the dosage on an existing medication can affect all aspects of your body’s well-being, including your menstrual cycle — that’s why your doctor, including your gynecologist, always wants to know each and every medication that you’re on.

5. Weight Issues: A major change in your weight — either by gaining a lot or losing a lot of weight — can throw your ovulation cycle off. People who are underweight or extremely overweight sometimes don’t have a period at all — which is not very healthy. Overall, an incredibly wonky or nonexistent period is a sign of possible health issues.

6. Exercising Excessively: Have you been hitting Soul Cycle every day after school? Training for a marathon? If you’ve taken up a new and intense exercise routine, your period might be thrown off. In fact, people who engage in extreme physical activity sometimes see their periods delayed.

7. Miscalculation: The average menstrual cycle is 28 days, but many, many women have shorter or longer cycles and don’t chart them correctly — so it may be that your period is not actually late. Additionally, the majority of women have cycles that are irregular and don’t necessarily realize it. If your period is early even by a few days one month, it may arrive late the following month.

Visit a doctor to find out why.

Though it might be because of your daily food intake (too little nutrients).

However, don't worry too much about this as you are still going through puberty and the duration between each periods haven't "settled down" and is still changing.