I have lower back pain but why?

That's right. I get a consistant pain & that seems worse if I stand in the same spot for too long. It's to the lower region of my back right above my hips but on my left side of my back. What can this be? I would put it down as posture or something but it's brought on whenever I don't eat for some time during the day. If I take a deep breath it becomes slightly tighter & then I can feel the pain more.

I have Acne & gilberts syndrome & I am underweight at 125Ibs (about 8/9 stone) & I am 6 2" tall.
I don't smoke or drink. Tweet