Baby is growing so it is normal. I had it when I first got pregnant and through out my pregnancy.
If this is your first baby it could be round ligament pain. With my first 2 it was very painful to sit, stand, or walk. It was painful inbetween my legs and my hips and my back and my pubic bone. And its all normal. Try taking a warm bath and Tylenol. It might help a lil.
How far along are you? I am 33 weeks and am definitely experiencing it. I have been told by several different people it could be round ligament pain, could be the baby moving down and his head's hitting the cervix or just natural pregnancy pain.