Try a chiropracter or osteopath – I personally prefer chiro – and see what they recommend.
Generally, cyclists have absolutely rubbish core stability and upper body strength, and this can lead to all kinds of malarkey.
I have a screwed up lower back (SI joint) at the moment – it returns every few years – and chiropractic treatment helps it, as does regular pre-ride stretching. Apparently a healthy dose of Pilates, as tomthumb suggests above, is an excellent preventative measure. It’s worth seeking out a chiropracter by personal recommendation (or look for an AECC – qualified dude) and spend some money with them. If they reckon you should come back every week forever, then don’t go back. Most will treat you weekly for a couple of months *max* before you’re fixed. I usually am right after two 20 minute sessions – it’s money well spent.