Low back pain between rides - none during?
Before I consult my doctor, has anyone experienced this kind of pain? The pain is located around the lower back, radiating towards the buttocks and no further (i.e. legs feel fine). It's a tolerable but deep nagging pain (always there at low intensity), i.e. tolerable enough until I do anything that stretches my back, then it hurts really bad. I've had sharp pain before in the lower back and I know how that feels, but this is something new to me.
It started yesterday morning. The night before that I did an ordinary 1.5 hour ride, there was no pain during or immediately after this ride. I woke up yesterday morning with the dull pain. Then yesterday afternoon, I rode again. Thought I'd just try it and quit early if the back hurt. Surprisingly there was ZERO pain on the bike. So I did my usual 2.5 hour ride with no discomfort at all. Today, the pain is still there, but no worse than yesterday.
I usually can tell what caused a body pain but I don't remember doing anything that might have caused this. I didn't increase my distance over my usual, between 1.5 and 2.5 are regular rides for me.
Help? Any ideas? Any past experiences?