Hello, Thanks for writing to us. Irregular taking of birth control pills may create risk for pregnancy. You should be regular on taking pills. If you did unprotected sex just 3 days before expected due date, then chance of pregnancy is quite low. However, it needs to be confirmed by home pregnancy test. Hormonal imbalance and mental stress can cause late period with light spotting. These are the most common causes. On Negative test, reasons of late period are PCOD, hypothyroid state, over weight/ extreme loss, emotional upset, eating disorder, high prolactin. Here, I suggest you to undergo complete hormone profile (LH/ FSH, serum prolactin, progesterone, thyroid, DHEAS, testosterone etc) and pelvic ultrasound scan if you don t get your period after 1 week waiting. Review with test results or you can consult with local gynecologist. You may require hormonal pill to induce period. Maintain genital hygiene, control body weight. Good luck.