Thanks New, I do try to have days free of them as often as possible, (or only take a dose at night), so I don't get tolerant to the point where I get really bad headaches when I don't take them. I usually do get headaches quite often (I expect linked with the codeine and probably dehydration too) which I then took codeine for, of course.
I've had fewer headaches overall since I started this WOE, presumably because I'm drinking loads of water, and none at all this week without the codeine! 
captain thank you. I think it's a combination of things. Firstly my state of mind makes a big difference in both how much discomfort/pain I can tolerate before I reach for the painkillers, and also in my posture (which then exacerbates my back pain if it's bad). When I'm tense and low I've realised how much I hunch and slouch, and I think my pain threshold is lower. When I'm feeling good mentally I will put up with more before I pop the pills. Also, when I'm feeling better my posture is more naturally open, and I make more of an effort to stand and walk well, correct my posture (I have a curved spine so I'm a bit wonky) and do my stretches/exercises. I wish I had as much oomph and dedication to exercise as New has, but I'm a lazy cow. 
I used to take them most nights, too, as I don't usually sleep well and then the pain would niggle at me. But since I started this WOE I've been sleeping ever so much better, so have cut that out too. 
All hail low carbing and Bootcamp!