Hello,
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There could be two possibilities in your case.First it might be posible that you are pregnant and the hormonal levels are low so the test is not showing up.You can consider repeating a test now.
Another possibility is of some hormonal imbalance in the body due to any underlying abnormality as PCOD,pelvic infection etc.But a detailed pelvic examination and investigations only help in knowing the cause.Kindly visit a Gynaecologist for evaluation.
Take care!