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Chances of pregnancy due to contraceptive failure cannot be ruled out completely as suggested by your recent symptoms. Hormonal contraceptive pills use can also lead to shorter and lighter periods. However, if pregnancy is suspected, visit 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). Stop the birth control use if you suspect chances of pregnancy or if pregnancy gets confirmed. 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.