A missed period with a negative pregnancy test can occur for several reasons, including hormonal imbalances, stress, thyroid disorders, polycystic ovary syndrome (PCOS), significant weight changes, excessive exercise, certain medications, or natural variations in the menstrual cycle. Home pregnancy tests are most reliable from the first day of a missed period or at least 21 days after unprotected sex. If the test was taken too early, pregnancy is still possible because hormone levels may not yet be high enough to be detected, so repeating the test after a few days may be helpful if pregnancy is suspected. If your period is delayed by more than 2 to 3 weeks, or if you continue to have irregular or missed periods, consult a gynaecologist for a proper evaluation and appropriate tests to identify the underlying cause. Seek immediate medical attention if you develop severe abdominal pain, heavy bleeding, dizziness, or fainting, even if the pregnancy test is negative.