I had a similar experience - 4-5 years of pain (not just back, but RSI-style symptoms in hands and wrists). What ultimately "cured" me was not exercises, or better posture, or better equipment (though, I still definitely advocate for split keyboards and vertical mice), but realising the strength of the connection between the mind and body. I would find that any slight hint of pain would trigger a massive overreaction by my brain, due to the despair/anxiety of the pain coming back. This then made the pain worse (stress/tension/fixation and the mind "over-amplifying" the pain signals) which made for a very vicious cycle. 

After a few weeks of journaling, therapy, and mindfulness and breathing practices, my symptoms got a hell of a lot better. For the last couple of years, I've been basically symptom-free. Yes, I still get the old sore back or twinge in my hand, but as long as I reassure myself that this is normal ("everyone gets it"), it quickly resolves in minutes or at worst overnight. 

My working theory is that I had an initial injury (and there is a specific incident I can trace it to - a new job with an employer who didn't take my complaints as seriously as they should've) that was then prolonged by *years* because of my (perfectly reasonable) emotional response ("what am I going to do for a career" etc) that meant it never resolved even after the physical injury itself had. There's a lot of discussions online around the mind-body interaction --- one interesting theory is that the brain essentially lowers the "pain threshold" substantially so that you become hyper-sensitive and your nerves are firing for very gentle pressures/stimulation. 

I am a very scientifically-minded person (it's my profession, even), so this sort of hypothesis/diagnosis felt a bit like quackery to me for a long time. I guess I eventually tried out of desperation - and it turns out that my doctor and other medical professionals were very receptive to it, saying that it was something becoming much more widely accepted in the medical field (the mind-body interaction). I suggest finding a GP who is up-to-date with research and who can help you to understand if any of what I've said fits with you as well.

Good luck - I promise it gets better. I remember people telling me that too, and me being unable to believe that it would be possible. But it truly is.