Every woman might have an irregular period at least once in her lifetime. Irregularities in menstrual cycles have different causes and hormonal imbalances are among the most common. Changes in hormones might occur because of stress or little sleep, too much exercise, weight gain or loss, or changing contraceptive pills. That's why it’s common for young girls and women approaching menopause to experience irregular menstruation. 

There are other causes of irregular cycles

• Using certain meds 
• Having an IUD (intrauterine device)
• PCOS (polycystic ovary syndrome)
• Ovarian cysts
• Return of the menstrual cycle after pregnancy   
• Extreme methods of contraception
• Thyroid problems (overactive or underactive)
• Fibroids or polyps of the uterine lining 
• Thickening of the uterine lining

Your period might occasionally come earlier than usual, but if it continues to occur chaotically or with delays of over 7 days, you should see your doctor. 

Sources:

Why Is My Period So Random?, webmd.com

Irregular periods, nhs.uk