My period came two weeks apart what is the cause?

Irregular ovulation: If you are not on birth control pills then you probably ovulated irregularly this month. If it continues next month i would recommend a visit to the obgyn and consider checking your thyroid, an exam and possibly an ultrasound.

Not sure: 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.