What should I do with my son I don't know what to do?

I have a 8 year old son and he broke his leg the last monday(tibia in two places, 2/3 of the length), he got his permanent cast on wednesday morning and the problems started. He had been in some pain since he has got the cast, we thought the pain was normal the first two days but the pain don't go down, his teacher called us on friday to pick him from school because of the pain. In the day he has little or no pain, but when he goes to bed, he fells asleep but at dawn he wakes up crying in pain, he wakes up with pain every morning since he has the cast, he said us that he doesn't sleep much at night. we revised his bed, put some pillows and soft cushions there, we make sure that our son doesn't wake up and try to walk at night, but we didn't solved the problem. We know that we should ask this question to his doctor, we have an appointment on tuesday, we are very concerned and we want to know something until your doctor check because we know that can not be happening, tuesday is far and our child is in pain. Please answer, we thank in advance for all your answers.