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The symptoms (progressively delayed and lighter periods, spotting, abdominal cramps, low back ache, mood changes, bloating, changed mouth sensations/metallic taste, appearance of blue veins on breasts, Montgomery tubercles around areola) could suggest possibility of pregnancy. If pregnancy is suspected, look out for development of any other new symptoms suggestive of pregnancy and consider visiting your gynecologist at the earliest for thorough examination (to confirm pregnancy related changes/signs in body) and blood/serum HCG level test (to confirm/rule out pregnancy accurately). Sometimes urine pregnancy tests can keep showing you false negative results during early pregnancy as the kits are calibrated ones, so unless the hormone levels in urine reach a certain level, they do not show positive results. Consider being in regular follow-up and monitoring of your treating gynecologist and report any abnormal/new symptoms immediately. Take adequate rest. Drink plenty of water. Maintain healthy diet.
Take care.