Hello, Thanks for writing to us. If you did unprotected sex on above mentioned date, then you have LOW to MINIMAL chance of pregnancy. In this case, I suggest you to undergo one blood test for beta-hCG to rule out late conception as early test may be sometimes inconclusive. In absence of pregnancy, other reasons of late period may be due to PCOD, ovarian cyst, hypothyroid state, over weight/ extreme loss, extra mental stress or anxiety, emotional upset, eating disorder, high prolactin. You should undergo complete hormone profile (LH/ FSH, serum prolactin, progesterone, thyroid, DHEAS, testosterone etc) and pelvic ultrasound scan (USG) to identify underlying pathology. 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.