What Causes Brown Secretion From The Vagina With Severe Abdominal Pain After Taking Norethesterone?

the doctor tols me to take norethesterone 5 mg 2 times daily starting from 30 october since my last periode was in 5th october....... i had small amount of spots of blood and brown secretions since 2 days so i took norethisrone 5 mg yesterday thinking that it is not the periode and today i had a very sharp pain in my uterus and more blood but not heavy> i want to stop this period before friday.... will i stop the medication to let the menstruation go on? or continue it? please answer me quickly... thanks