Hormonal imbalance. If you did the test correctly at more than 5 days after a missed period and it was negative, you are unlikely to be pregnant. You may re do the test in 4-5 days unless you get a period by then. Use first morning urine and follow the instructions for the test carefully. If you do not wish to be pregnant, use contraception all the time, every time. You may consider implanted contraceptive, or IUD. Practice safe sex.