My lower left side of my back has been hurting every day for the past week, is it a kidney problem?

Back pain. It might be, but it could also be a problem with the muscles in your back. You need to see your doctor to have your urine tested to check for kidney infection or kidney stones and have your back looked at to check for a muscle problem.
Possibly... One's kidneys are located on both the right and left sides of the lower back, so having pain in the area could be caused by the kidney(s). However, there are many other possible causes to low back pain. The only way to narrow the possible causes is to seek the evaluation of your physician. He or she can run some simple tests to make a better determination of the cause.