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If the time of your unprotected intercourse is around your fertile days or close to ovulation time, chances of pregnancy are possible as suggested by your symptoms like shorter/lighter periods, dizziness, nausea. Look out for development of any other new symptoms if pregnancy is suspected. If you suspect chances of pregnancy, 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). 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.