We see many clients each week who have foot problems that contribute to their ongoing back pain. Ensure you have your feet and legs checked to see if they are part of you problem.
Every week I see clients come into my clinic with a bag of orthotics that have not worked for them. I myself had been frustrated with the orthotic results I got for my clients until many years ago when I found a better way to design and make orthotics.
You may not think it but your feet can play an enormous part in your enjoyment of cycling. The right sorts of cleats, bike shoes, foot position, movement of the foot all determine how the force you generate is transferred into the bike.