If you are suffering from an uncomfortable pain in your mid back or lower back and this pain has been going on for a while, it doesn't necessarily mean it's a back problem. It could possibly be the sign of a kidney infection or maybe your back has experienced some other trauma.
However, there are some obvious signs that it's a kidney infection including blood in urine (not always visible), burning during urination, nausea or fever. If you have any or all of above then you should go and see your GP as soon as possible.
Your kidneys are located on both sides of your spine, just above your hips. This area would probably feel tender, sensitive and localized to this area, but it can also move up to the waist area especially if you have a kidney infection.
If your problem is from lower back pain after you pull a muscle, herniate a spinal disc, or straining your back then you have the answer for the pain. So it will not be from a kidney infection.