There is all sorts of interesting research into pain medications going on at the moment. Sadly, it appears some of them can actually make you more sensitive to pain if you take them for extended periods--which is a no win situation for those of us with chronic pain. I do know that much as I enjoyed it, codeine wasn't a good choice for me. When it wore off, I'd have the miseries big time. I used to take 30mg maybe once a week to give myself some relief if I'd over done things. It worked a treat, but 6-8hrs later I felt worse than before I took it. Go figure.
I'm thinking of pushing past my GP now and getting some specialist advice. The issues I've had for ten years will never go away, and a combination of treatment side effects and aging mean that I'm developing a whole new suite of 'ouch;'
Pain Australia www.painaustralia.org.au is a good place to find 'proper' information about the meds you are taking. It's not an easy website to navigate, but you might find some useful things on there.
Mxx