I am guessing that the GP gives a general overview of your condition in a very brief examination, vague back pain is likely to be nothing but with a chance of being everything.
If you returned as the pain grew worse or continued, I am sure a referral would have come to the correct diagnosis and...
The problem when offering performance opinion on treatment received is that unless chronic or terminal it WILL get better no matter what treatment you resort to.
So for most of us, whatever treatment we seek, we are likely to conclude it worked !!!
I have used all of them, some good and some bad.
My conclusion is to find out the cause of back pain by a CHARTERED physiotherapist.
I used to think the 'cracking' of my back was a sure sign that my Osteopath was dealing with my sciatica, got a feeling it might not have done anything to help.