My spine is trashed. I think I did it early in life playing football. I know this condition is true because I happen work in a medical imaging business where we image ourselves often as a course of testing the equipment, with no negative repercussion to ourselves, or expense.
I have no discs remaining in the Sacrum-thru-L3 spaces, as they have all previously ruptured, and dessicated (on their own without surgery). I was lucky to have no ruptures that squirted out too much laterally onto the spinal chord, causing impinged nerves and more than a small amount of sciatica. There is also a lot of bone degeneration, but I have no idea why that happened.
I say all of the above, not as an appeal for group pity, but because I want to relay that have very little, if any, back pain when riding. In fact, most of the time when my back isn't feeling all that good, a few Vitamin I (Ibuprofens) and a good long, all-day ride is just the ticket to get it feeling better. I have occasionally had issues further up in the cervical area, but that is more acute, feels muscular, and probably due to not exercising enough, rather that any physiological decay.
While others may poo-poo the idea, I think the biggest difference for me was when I learned to ride bikes in the MYRP. Do not be confused here: I have not mastered it fully to this day. It is always a "work in progress" to feel the weight of your torso on your hands, and then transfer that weight onto your legs, torso and into your feet. It is totally non-intuitive. But it is so worth it. Practice makes perfect, and is also perfectly fun
Keep working on your riding position. Get your bike ergos adjusted to your own physique. Do not be dissuaded by the ignoramus butt-heads that will tell you that you are just a wimp for not riding the bike the way it was delivered from the factory, with ergonomics adjusted for some little Japanese 4' 12" guy, just because they happen to be able to put up with that. They must be very happy, because, as we all know, ignorance is bliss.
Riding is about enjoyment, more than anything else. Don't let anyone else's need to self promote cause you to lose any small part of that enjoyment. One day, if you keep it up, it will all click, and you'll be comfortable. And then you will be so glad that you stuck with it.
The down side is that you may not want to do anything else with your life from then on. Sorry. But welcome to the enigma.