is a regular 21 day oral contraceptive.
menstrual irregularities are common in women and it may not always be associated with use of contraceptive pills.
however if you had heavy flow perviously oral contraceptive pills
regularise the flow.
donot worry about it as long as you donot have only spotting or comlete absence of periods.
if you however feel anxious i would advise you to consult a gynecologist in this regard.
i hope i have answered your query.