It's good to get angry when someone, or something, fucks you off, but then try to let it go, hang onto it and you have an excellent excuse to relapse. Sparkles is sorry your family seem so unaware of the problem, sometimes it's a way for them to cope with the situation. If they can't see a problem, then there isn't one, simple. The mate he met the other night, is he close by, can you talk to him regularly? He seemed to be understanding of the situation, listened to what Nutellajunkie was saying.
It may seem like a long way off, but he has his doctors appointment to use in his favour. Try to think of all the issues that are troubling you, make a list if necessary, and take that. Ask what practical support is available, see if he can refer you to a counselor/psychologist to deal with his anxiety and his self harm issues, be totally honest with him. Nutellajunkie said he's a good doctor and he feels able to talk to him.
One big point, have his doctor flag his medical records just advising other doctors in the practice to be cautious when considering prescribing pain meds, especially codeine. Some doctors will prescribe codeine to former opiate addicts believing it's a safer drug for them to use. Giving it to someone who has been addicted to it would be insanity, especially if they were only complaining of toothache, but they forget it's as difficult to quit as any other opiate type drug. Giving you Solpadol would be the equivalent of a doctor giving Sparkles pure heroin.
Sparkles is so glad you managed to get past his anger at the fuckwit doctor, don't allow anyone to bring you down, the only person you should take notice of now...
is you. That's why you quit drugs, so you didn't have to allow a substance to rule every part of your life, didn't have to rely on it to calm you down or lift you up. Now...that's your job. And may I say, I think you're doing it excellently luv.

Stay strong sweetie.

Sparkles.
Don't forget, if you need to talk PM me. Hell, PM anyone here, that's one thing DF isn't short of...
support.