After reading your symptoms i would like to iterate that what you are going through are the withdrawl symptoms of norethisterone
Stomach and back pains along with headaches
are there as pre menstrual exagerated symptoms which will subside as soon as you start with menses.
Meanwhile you can take symptomatic treatment such as muscle relaxants and pain killers.
If your problem does not subside i would strongly recommend you to visit your doctor for the same.