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Shorter and lighter periods could be a sign of pregnancy (other causes include anemia, dehydration, hormonal imbalance, changes in lifestyle, eating habits or exercise levels, etc). It is also not uncommon to find women getting pregnant while being on hormonal contraceptives. If you suspect to be pregnant, consider visiting your doctor/gynecologist for further examination (to confirm pregnancy related changes/signs in body) and blood/serum HCG level test (to confirm/rule out pregnancy accurately). Take adequate rest. Drink plenty of water. Maintain healthy diet. It is difficult to comment on your symptoms without examining you. Look out for development of any other new symptoms suggestive of early pregnancy.
Take care.