Should I Continue Taking Progyluton For 21 Days If I Got My Period After 6 Days?

Hi , Im 30 years and have 1kid ...facing irregular periods. So doctor said to take progyluton for 21 days and periods will come after 3 weeks but I taken for 6 days and got my period now ....pls tel whether I need to continue the tablet or STOp and say why it happened