What Causes Stoppage In Menstruation?

Im 26 years old. Ive had a procedure done 6 months ago called a colposcopy due to possible cancer cells. I bleed for two weeks thinking nothing of it because my period was supposed to be due. Right after I did not get my perios for 6 months. The doctors told me this was due to my birth control pill which I have been taking for years and its never done this. Is this normal? Could something have gone wrong?