been there!
got any pain shooting up the back of your legs or any numbness any where? my back trouble comes from work not bikes! but after the best doc's have to offer and 16 weeks of P/T it comes down to strech, strech and more steching for me. mine was due to the bottom of my spine starting to fuse slightly because of lack of streching and movement in that part of the back, plus, my ligament are kinda tight from the "university strech";) but if you can afford it or have good insurance, go see you trusty back doc ! good luck.