Write, I used to have some debilitating back problems and my (yoga teacher) sister told me she learned that back pain was caused by anger. (and of course, my lack of flexibility and muscle tone!) Needless to say I was pretty angry at her for saying that, mostly because: for the previous 5 months (and it continued for another 5) I was carrying my partially parylized golden retriever around in a sling. She could not understand this at all, as many people probably could not, but my dog was not in pain, she simply couldn't use her back legs. I made a choice.
I must say that in retrospect, I did carry lots of emotion and people's pain (and animals!!) and there is no question in my mind that it's connected. I was mad, and part of it was that my precious dog was in this state, and my husband at the time was a SH** and and and...
Anyway, now, rather than get down on myself ("oh, what's wrong with me, my back hurts") I realize now that when my abdominal muscles are weak, my back hurts. When I put everyone else's needs ahead of my basic ones, my back hurts.
Plain and simple. When I am strong, and exercising regularly, I only hurt from using muscles, and that's a good pain.
So, maybe don't worry about "what" is causing it, and go for a brisk walk and get stronger....(as I sit here typing instead of exercising!!)