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Stomach cramps and cold/flu like symptoms could be symptoms suggestive of early pregnancy. Look out for development of any other new symptoms suggestive of early pregnancy. Wait and watch for your periods. If you suspect to be pregnant, visit your doctor/gynecologist at the earliest for a thorough examination (to confirm pregnancy related changes/signs in body) and blood/serum HCG level test (to confirm/rule out pregnancy accurately). Urine pregnancy tests can show false negative results during early pregnancy and if tested early in pregnancy, hence they cannot be relied upon for accuracy.
Take care.