What Are The Side Effects Of Using Norethisterone?

I was prescribed Norethisterone to help regularize my periods after a year of using Implanon and months of painful heavy bleeding. I completed a 10 day course 5 days ago, and have had extremely heavy bleeding for the past 2 days. Is this normal, and how long is it likely to last? I was also given a 3 month prescription of Microgynon to take if the Norethisterone didn t work. Should I begin taking this now or do I need to wait, and if the latter, how long for? Thanks for your help.