It is possible that a pregnancy test can show a negative result when you indeed are pregnant. The reasons could be several: it could be a defective test, past its expiry date, or wrongly manufactured. However, your body could also not produce the required amount of the hCG hormone to trigger the results as positive. The best thing to do is visit a doctor and ask for a blood test in all these cases. With high chances of certainty, they are the best way to be entirely sure, and you can do it easily at any clinic. Consuming other medications that might have affected the test results could also be why it is showing wrong.