If you have not had intercourse, then this delaying of periods
can be due to conditions that affect the ovaries
, uterus, hypothalamus, or pituitary gland. It could be hypothyroidism, post pill amennorhea , polycystic ovarian syndrome or less frequently a pituitary tumor causing high prolactin levels or a hypothalamic disease. Seek a gynaecologist immediately who will take a careful medical history ,a physical examination and investigations.
I hope it helps.