How long does it take for a broken thumb to heal fully?

I broke my thumb about a year ago. It is still bothering me and hurting. I can bend it a lot more but since I am doing my GCSE's this year I have to do a lot of writing. I have adapted the way I hold a pen/pencil because I can't bend my thumb enough to hold it the way I used to. It really aches and is painful when I write for not that long at all. Does anyone know when this will stop? Or what could be wrong with it?