I'm 13 weeks pregnant almost 14 and I've been having major back pain for the last 3 days. I've read that it could just be because the babys growing, but I know it doesn't weigh more than an ounce right now and I don't think that's enough pressure to cause the amount of constant pain that I'm having. Is it because my uterus is moving? Is this normal? Or should I go see a doctor about it?