Hi there :
I think this is a referred pain
from viscera ( gall bladder
and so on). I guess what I am trying to say the low back pain
is not from your back likely, rather it is from other reasons ( hepato-biliary system) but this what you feel at this moment.
Furthermore, I would like you to see if the back pain radiate ( referred to your legs)/ as well if this related with prolonged standing or to the body position. such info might help to verify wether these symptoms from back originally or referred to your back from other reason.