The duration of the menstrual period is highly individual. A "normal" cycle duration is considered to take from 3 to 7 days. Periods during the usage of birth control pills are not real periods because the body does not ovulate while using contraceptive pills. This period of yours was a real period but the next periods will be false. Maybe they will last shorter than 8 days; you will have to observe and record the periods on a calendar and then consult your gynecologist with the data.