There are many reasons for this and they are related to pregnancy itself. As we gain weight, the spine curves, allowing the center of gravity to remain over the legs so we don’t topple over. This curvature in the spine keeps us stable so we don’t tip over, but it also causes low back pain. Sometimes a pregancy girdle will help with this.
The second common complaints are either SI (sacro-illiac) pain or pubic symphysis pain.
The SI joints are located below the belt line on the lower back and when we’re sitting, are just above the buttocks. The pubic symphysis is located in the front and is the hard bone where our thighs come together.
However, during pregnancy, we release a hormone called relaxin that softens the cartilage in our bodies. This makes all of those joints in our pelvic girdle shift a little bit more. These joints are normally non-moving joints so when they do shift, there is pain.
So, when we roll around in bed and notice pain, or walk and notice pain, it is just nature’s way of softening up the pelvic girdle so that there will be more “give” during labor.
Once we deliver, our pelvis does eventually return to normal. Until then, any movements that will un-balance the pelvis will cause pain: crossing our legs, standing with weight on one leg, walking quickly, sitting on one buttock instead of both, etc.
The short term solution is heating pads and limit movements that will unbalance the pelvis. So, we want to stand with weight equally distributed on both legs, don’t cross our legs at the knee, and when we roll in bed, put our knees together and roll the pelvis out of bed as a block, instead of swinging one leg out of bed at a time.
Bottom line: normal but uncomfortable, and temporary