YESSSS! This is a wonderful idea, and not only will it help the doctor to help you, but it is so beneficial for you as well. During my really deep knee issues, having one surgery after another, I started a journal and it helped me to look back and see what triggered the most pain and also let me be able to read about the "good days". Seeing the "good days" helped me to realize that not every day had been a bad day if you get what I'm saying. Good days to me, are when my pain is only at a 4 as opposed to a 7 or 8.
You are right, the pain scale is a good thing, but there really is so much more to your pain. Some days your pain could be a 6 and it could be burning, throbbing pain, and the next day it may still be a 6 but the pain may be more of a stabbing constant pain. Any information you can give your pm doctor should help him to understand what you are experiencing.
I felt that writing about my pain was theraputic as well because it allowed me to vent without getting the usual, "you just have to be patient", or "you have to tough it out", from friends/family who were trying to help, but just didn't understand what I was going through. I could write anyhting I wanted in my journal without holding back.
I hope you find that writing your daily journal will help you and your doctor. It is a great idea. Please keep us informed. I'd love to know how it helps you.
All The Best-