What Causes Prolonged Bleeding Inspite Of Being On Birth Control Pills?

i was prescribed adderall about a month ago, ever since i started taking it i have been having a period every two weeks that will last two weeks or more. i went to the gyno they said everything was fine and prescribed me birth control to regulate my periods, i have been on the birthcontrol for a little over 3 weeks and i have been bleeding for two weeks still since i have started it.