In addition to what most people have said DO NOT STOP PUSHING THE ISSUE. To you it’s life ruining and potentially life ENDING. To the idiots you dealt with “it’s just some kid experiencing back pain for the first time”. Additionally by backing down they perceive themselves as being correct.
This will suck but you really have to “bitch and whine” to high heaven to get these dense morons to listen to you. At the very least it might get them to seek treatment just to shut you up.
DO NOT GIVE UP, your adult self would kill you if you stopped fighting for treatment so keep pursuing it. If a doctor refuses you just have to find another. If you can afford it, a therapist would give you much greater empathy and some possible paths to help find a doctor who gives a shit and will try their best to actually help you.