I m 25 yrs old .i have taken tablet yasmin (drospirenone and ethinyl estradiol) 21 days..bt my menses not cum still.what is the reason.when menes come.?

Low dose: Low dose pills such as yasmin (drospirenone and ethinyl estradiol) stimulate only a little growth of the uterine lining so periods are much shorter and lighter and occasionally you skip periods. If you have not missed any or taken any late you can safely just keep taking them. If this becomes a consistent problem your doctor may add some additional estrogen for a time. If you have missed some, I'd recommend a pregnancy test.