Anyone else having this pain?

I read a lot about back pain in pregnancy and that is a daily fight for me... It is crippling. But I am wondering if anyone is having another pain that I haven't seen discussed on here. I am having TERRIBLE pain in my pelvic bone. Can't walk or even move sometimes. This isn't my first pregnancy and I remember having it before, but I'm only 16 weeks right now and it is so bad! But it comes and goes. One minute I am fine, the next I can't walk. 10 minutes later, I'm fine again. Anyone else having this problem so early? What is it? I assume it is my body moving and getting ready. Just wondering if that's so and if it's normal...