I am a 20-year-old man. My girlfriend and I engage in unprotected sexual intercourse regularly -we have sex thrice a month and never use protection. She did take a contraceptive tablet, but as far as I know, she has only taken this once. Her period is 22 days late this month, and we are, understandably, concerned about this. She has tested herself with a home pregnancy kit twice, and, on both occasions, the result was negative. However, we are still a little worried. What do you recommend we do to put our minds at ease?