Hi Dean
I have a couple of thoughts you may like to consider. I hasten to add that my experience is not the same as yours, but the lessons I learnt could be beneficial for you - and may even save you money?!
I have a recurrent back pain, eventually diagnosed as sciatica some years ago and believed to date back to my late teens and early twenties when I seriously over-dosed on sport in general and particularly with rugby. And fairly regularly 'crocked' myself as a result.
I had no real inkling of any long term damage until my mid-thirties, when the pain suddenly kicked in and left me - extremely embarrassed! - completely immobilised when I tripped going up some stairs. My GP said "pain-killers and bed-rest if really necessary", so I/we treated the effects, but the cause was never identified.
Several weeks later everything quietened down and all was quiet for another 4 or 5 years. After the next 'attack' it came back (ha ha) with growing frequency and pain, until about 5 years ago, when I finally bit the bullet and - quite expensively! - learnt a lot from osteopaths, physiotherapists and chiropractors.
In a nutshell, and indeed as others have already said, "posture, posture, posture" is the message. The human body is phenomenally adaptable, and extraordinarily adaptive. A huge amount of bad posture, over-exertion, etc etc, is absorbed but eventually your limit is breached.
By all means experiment as suggested above with different positions (!!), but I would also recommend that you get a specialist (osteo/physio/chiro....whatever) to check it out - your GP is after all by definition a General Practitioner.
Ask around, check with relatives friends for their advice and experience, and ask your GP too (I asked mine - eventually - and he said that as my GP he would prescribe pain-killers, but that his wife and his brother had both benefitted from seeing osteopaths for back pains - that was what really set me on my way to a better understanding).
Ignore it - the pain warning - at your financial and/or physical peril! I am resigned now to a monthly 'put it all back in alignment' session, and directly as a result I can and do lead a more active life now than I had been accustomed to for quite some years...but if I'd got it diagnosed and treated properly 20 years ago I'd have a lot more beer and new turning tools money in my piggy bank now!
Don't read this wrong - I'm not bitter, though I am of course arguably twisted (sciatica does that to folk!) - I just wish that either I'd asked a lot more about it 20 years ago, or that someone made me understand at the time about the 'stitch in time' aspect!
Here's hoping it all turns out (groan!) fine in the end.