Do you have a pain that you can point to in your lower back?
Don’t rush out to get an MRI, it is probably your SI joint. SI refers to the sacro-iliac joint. This is where your sacrum meets the iliac crest of your pelvis. This joint has a small degree of motion and the pelvis rotates slightly back and forth on the sacrum as you walk. It is common for it to rotate too much and be either anteriorly or posteriorly rotated (tilted) which is known as an SI dysfunction.
SI dysfunction can be provocative to the ligaments of the pelvis and can even displace a disc in the front of your pelvis causing groin pain. Why does this happen? I find that patients fall into 1 of 2 categories. Either you are (1) weak in the muscles that attach to the pelvis causing to much joint motion, or (2) have imbalance in tightness that attach to the pelvis causing torsional forces. One sided hamstring tightness is a prime example. We certainly see both situations where there is weakness and relative tightness.
Pregnancy can contribute or lead to SI dysfunction. Muscles hold the skeleton together, but so do ligaments. Ligaments are bone to bone attachments and are not elastic like muscle and tendon. They are more like pieces of duct tape keeping the pelvis together. When you are pregnant, your body secretes a hormone called relaxin that loosens the ligaments of the pelvic girdle in preparation for delivery. The ligaments do firm back up after delivery, but they are not quite like they used to be. So the more kids you have, the more likely you are to have SI dysfunction and pain. You may not have the pain right after pregnancy, but many years later. If the pregnancy loosens the ligaments but your muscles are in decent shape, you will probably be asymptomatic. Then later in life if you become sedentary and your muscles atrophy, symptoms will begin because both the active and passive systems (muscles and ligaments) are loose and now the skeleton is unstable.
The good news is that it is relatively easy to fix without surgery or medicine. You can use what is called a “muscle energy technique” or MET for short. It takes advantage of the muscles that attach to the pelvis. By isometrically contracting them, you can place a force on the pelvis to help put it into a more neutral position. See below: