I have been riding road bikes for about 7 years and it wasn't until I started racing as an amateur that I got lower back pain from strenuous rides. I saw a chiro for a few months, tried yoga, but it kept coming back and was affecting my quality of sleep.

Turns out it was my saddle height the whole time - even after getting a bike fit, my saddle was too high which was causing the pain. Might be worth a look for you!