Hi and thank you so much for this query. I understand the anxiety delayed periods bring especially when you are not ready for a pregnancy. The most common cause of missed menses in a girl of your age is pregnancy and more so with a history of unprotected intercourse. It is difficult to tell if for real you are pregnant or not without doing a simple urine pregnancy test. Take one and let s see what the results are. If they are positive, then you are pregnant. If you are not, then staying calm and relaxed would be the way forward. It is not to uncommon to get delayed menses without any real cause. Please, withdrawal before ejaculation is good but a very poor method of contraception with very high failure rates. Consider talking with your doctor and adopting a more reliable contraceptive method. I wish you well and the best of possible outcomes. Thanks for using our services and feel free to request for more information if need be. Dr. Ditah, MD