Lower back pain

I'm currently 12 weeks pregnant with my second child. With my first I had really bad sciatica at about 28 weeks. The last few days I've had extreme lower back pain, I thought it might be because I was wearing shoes with a little bit of a heel the other day. But it still hasn't gone away. Any suggestions on how to deal with it or ideas of what it might be? It doesn't feel like sciatica. Thanks in advance!