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Your symptoms are suggestive of pregnancy. The pregnancy if suspected should be confirmed with examination and blood HCG test done by a gynecologist. If the blood HCG test comes back negative, it will confirm that you are not pregnant.
Visit your gynecologist for a thorough examination and blood HCG levels to confirm/rule out pregnancy. It can detect pregnancy accurately as early as 11 days post conception. Urine pregnancy tests can keep showing false negative test results due to less concentration of pregnancy hormone (HCG ) in urine.
Take care.