Thanks for the query.
That can be due to hemodilution
because of anemia
Better to get tested for hemoglobin
And depending on the percentage of hemoglobin start taking treatment.
In case of severe anemia you may need intravenous iron solution infusion or blood transfusion
So you consult your doctor once and get examined.
For more details you can ask me through: http://www.healthcaremagic.com/doctors/dr-sree-gouri-sr/63429