Why is my period so irregular?

Probably normal. Have you ever been regular? When you first start getting your period it is very normal for them to be irregular as the hormones that cause this are in the process of reaching a balance. Given your age this seems most likely. You can also go and see your gynecologist if this is more of a concern.
Many possibilities. Usually the first 2 years after your first period is a time when your menstrual cycle is irregular due to the system in the brain that signals your body to make certain hormones. This system takes time to mature and regulate your cycle properly. This can take up to 2 years. If your period is still irregular beyond this time farm you should be evaluated by your doctor for a hormonal condition, PCOS.
Hard to tell. If you have always had irregular period that can be normal for you. It is always a good idea to see your doctor and get checked to be sure. Then you both can decide if anything needs to be done about it in your case. Diet, medications, exercise and sometimes stress can have a role too. Go over all this at your visit.
Many reasons. Your period is like a canary in a coal mine and is easily disturbed by many things including stress, extreme dieting or exercising, thyroid problems, diabetes or insulin resistance, polycystic ovarian syndrome, medications. When it is irregular, your body is telling you that you need to see your doctor to find out what is going on. It may be just because your hypothalamic-ovarian axis is still maturing.

Related Questions

Why is my period so irregular? I need some advice.

Need GYN eval. Reasons for irregularity include weight gain or loss, breastfeeding, alcohol use, eating disorders, marked emotional stress, endometriosis, uterine fibroids, cervical polyps, polycystic ovarian syndrome, excessive exercise & pregnancy. When a girl has just started menstruating & around the time of menopause periods can be irregular.

What are some reasons why my period is so irregular?

Possible reasons. When a girl has just started menstruating & around the time of menopause periods can be irregular. Other reasons for irregularity include weight gain or loss, breastfeeding, alcohol use, eating disorders, marked emotional stress, endometriosis, uterine fibroids, cervical polyps, excessive exercise & pregnancy.