The doctor has asked you after only seeing your current x-ray. Once the bones are joined than it is important to start the weight bearing so that your bone in that area become stronge and the muscles which become weak because of not using it becomes strong.
Now walking with full load will be difficult in the start, it would be good if you start with partial weight bearing and than inceasing it slowly to full weight bearing.
As far as pain is consider this will be there when ever you will start this weight bearing process, even if after 2 months. This is mainly because you are not using that portion of the body and once you start using that it will take some time to come to the normal stage, but you have to bear the pain and if pain is too much, consult your doctor and ask for pain killers or some physiotherapy
before doing this.
Thanks and take care