Suggest Treatment For Irregular Periods

my dr prescribed me regestrone to start my periods ,she adviced me to take regestrone 3 days and then contraceptive pills on 5th day of the menstruation for 21 days. and repeat the same after a gap of 7 days.she told me to this for 6 months...but after 6 months my periods are irregular...what do i do...do i again repeat the same ...is there any side effect of continuing these tablets....