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The symptoms (altered periods, lighter bleeding, bloating, abdominal cramps, nausea, fatigue, sensitive nipples) could be few of early symptoms suggestive of pregnancy. Look out for development of any other new symptoms if pregnancy is suspected. If you suspect chances of pregnancy, or if the symptoms have been persistent, or if the periods are abnormal, consider visiting your doctor/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). The urine pregnancy tests done very early in pregnancy can show you false negative results as the kits are calibrated ones, so unless the hormone levels in urine reach a certain level, they do not show positive results. Be in regular monitoring and follow-up with your treating doctor/gynecologist and report any new/abnormal symptoms immediately. Take adequate rest. Drink plenty of water. Maintain healthy diet.
Take care.