It might not be medication that you need. I have been having a similar problem, although not with my back. Physio isn't helping with the pain, which is affecting my sleep, my concentration and my temper, and makes it impossible for me to drive, brush my hair, dress myself, and a load of other things that I used to take for granted. I've now been referred to a consultant neurologist to see if we can work out what's causing it.
I suggest you go back to the GP and ask if they could refer you to a specialist in pain management, because you don't want to take pain killers indefinitely, and the situation is becoming unmanageable.