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If the blood flow is normal and there is no change in the pattern and duration of the menstrual cycle then possibility of pregnancy is ruled out.The symptoms as headache and dizziness can be due to other reasons as Blood pressure changes,blood sugar fluctuation,ear issues,gastric problems as acidity etc.
If the symptoms are persistent then consider visiting a Physician for detailed evaluation.Consider monitoring your Blood pressure for few days.Have healthy balanced diet and take adequate rest.Avoid any strenous activity.
Take care!