Hi Rylek
I've had similar problems, over the summer last year I had slipped into eating nuts as a snack, which really irrated my kidneys.
What I have found is that it's a combination of things and have been back to the doctor several times for tests. One thing that is free on the NHS but the doctor has to refer you is to see the physio, which has helped to strengthen my back muscles, do you find your back worse at certain times of day, or is it a constant.
I would also recommend Rolfing as I went several years ago and had some Hellerwork, which is the best treatment my body has ever had, it is worth saving up for if you can.