Having read the posts again, you may have a similar problem to what I had. About ten minutes in to my run my lower back would start to ache, It would get worse as I went on but would be gone within minutes of me stopping. It became bad enough to stop me running most times, by which time I was running like an old man at the speed of a crippled tortoise. Eventually I stopped bothering to run as I ended up walking so much.
One day after playing football the pain wouldn't go away, so I went to hospital, and was told it was a suspected herniated vertebral disc, and to go to my GP on Monday. As I'm only 24 I was gutted. I then went to an osteopath for a second opinion. He told me that it was nothing to worry about, just that to of vertebrae were stuck together
. I hobbled into his clinic like Herr Flick of the Gestapo and bounded out normally
, if slightly sore. A few days later I was fine and running. I'm still trying to lose the belly I acquired though.