First, you'll need to determine if it's your kidneys or your low back muscles causing the problem. (If it's your kidneys causing the pain, you'll need to see a physician) Your kidneys are about halfway between your spine and the side of your body and behind your lowest rib (see diagram at http://www.pbiv.com/images/nature/kr/location.gif).
If it's not your kidneys, it's possible that you've strained your low back (quadratus lumborum) muscles and they've become hypertonic (overly tense). At the low back on each side of the spine and going down to the hip bone is where the quadratus lumborum muscles are (see diagram at http://www.floota.com/images/QuadratusLumborumDiagram.jpg ). When we overuse those muscles, they can get hypertonic and cause pain when bending over, sitting, or standing for a long time. And when we have hypertonic muscles and tendons, it can create trigger points in them, which are spots in the muscles and tendons that are very sensitive when pressed. Many times, trigger points will give you pain in the area and even in other related areas (referral pain).
The best treatment for hypertonic low back muscles is Therapeutic Massage. Find a massage therapist in your area who's licensed and who specializes in releasing trigger points. Before making an appointment, ask him or her these questions:
1. Do you have experience working on trigger points?
If he or she does, then ask
2. Do you hold pressure on each trigger point until it releases?
While he or she is holding pressure on each trigger point, you'll need to breathe deeply and slowly to help each one release. If you find a massage therapist who works that specifically, you'll get the best results and it will be long-lasting. It may take a few sessions to get the problem close to 100% improvement, but you'll know immediately after the first session if it's helping you.
Once you get the tight muscles under control, it's a good idea to start stretching the muscles every day to prevent them from getting too tight again. Google "low back stretches" to find ones you can do, but don't do them until after you get a good bit of the tension out of the muscles and tendons..
Also, when sitting, be sure that you have a small pillow or some type of support that pushes into the curve of your low back. And when you're lying down, put a pillow under your knees to give your low back some relief. If you're lying face down, put a pillow under your abdomen for relief.
Ten years of experience as a licensed massage therapist specializing in therapeutic massage for pain relief.