First... flexibility can help alot of things. Lower back pain is one of them. If your hammies are too tight, they pull down on your spinal erectors.
As for rest, I'd say lay off deads (and squats, good mornings, etc...) for a while,or at least use very light weights. Let it rest, ice it, go to the chiropractor.
What activities do you feel it in? Everyday activities such as walking up the stairs and opening the refrigerator? or more excersize related activities?