I Have PCOS And Have Been Bleeding Since May, Most

I have PCOS and have been bleeding since May, most of this time bleeding extremely heavy which has left me feeling week and exhausted. I have had blood tests to check iron levels and they seem fine. I have been prescribed metformin to try and regulate my periods and mefanamic acid to reduce bleeding. I was recently precribed cerrazette to try and stop the bleeding which hasn't worked. I am now to try norehisterone. I have a history of migraines so certain pills are unsuitable. How long should i give the norehisterone tablets to work and what are my other options it this doesn't work?