It sounds tough but I can also see where your GP is coming from.
My MIL has the same conditions as you and her GP certainly hasn’t said no to strong painkillers - although I’m sure she has been very pushy so don’t know if that has made a difference - and she lives on them, also drinking quite a lot of alcohol with them every evening, going to bed late and then lying in bed for half the next day, hasn’t worked or for years and rarely leaves the house..
And looking at it from the outside - and she really is an unhappy and angry woman - it’s very hard to unpick what is physical and what is mental health, and the painkiller use plays a massive part in that.
I have no idea how she can tell what is going on with pain and her health, with a mix of such strong painkillers and hangovers involved, plus she is overweight and that is a consequence of not going out or moving, but she can’t go out because she is in pain but the extra weight makes her joints worse so the pain is worse… and so on. So she just seems trapped.
She was like that in her early 50’s when I met her. It looks very much like addiction and her the amount of pain relief she takes seems unchecked and it is as if it just can’t be questioned, or lifestyle changes considered, because she does have arthritis and fibromyalgia and says that is the cause of everything.
If she had a GP who had encouraged her to try other things and not let her head down that road, rather than just repeatedly giving out the prescriptions for the strong stuff, perhaps she would be in a better state mentally now.