It normally takes twenty eight days for the body to replace the expired tissues of a woman'swomb.This is aperiod of 14 days after the onset of ovulation.Many women go under this period differently,eg it only takes 21 days for them and others 28 days for acompleate cycle.Any abnormality or irregularity may be due to some diseases like Typhoid,STD/AIDS,malaria,CIRVICITIS,CHLYMEDIA,etc.These may lead to Pain with periods,irregulation,Heavy bleedings,No bleeding,servere headache, etc.If you have any qsn,put it across like atopic then i will reply on it