It could be simply mechanical, so caused by working one side of the back more than the other over a period of time. This can be caused by sitting at the slightest of angles at a desk or on long drives, or simply carrying everything in your right hand.
Is it possible you have a little pelvic misalignment or standing unevenly?
You can test the latter by standing as you normally would with a foot on a pair of weighing scales. You'll be able to tell if you carry your bodyweight unevenly by the readout.
Do consider eating more magnesium rich foods. This is a good time of year because all the beans, pulses, grains and root vegetables that supply magnesium are to be found in stews and casseroles.
Alternatively, take a supplement or magnesium citrate, malate, gluconate or taurate (all good forms).
Just bear in mind that while Arnica Gel works fast, Devils Claw's effects accumulate over time (a few weeks).