What Causes Prolonged Bleeding While On Contraceptive Pills?

im on birth control for about 6 months, i skiped my period about twice a month apart everything was fine until i realized i wasnt taking the right pill on the right day, but taking one everyday, so i took 2 placebos and started up a new pack and i started my period 3 days after starting the new pack and now 11 days later im still bleeding and it wont stop!! help!