Everything suggested above is great. I had sciatic pain from a sporting injury when I was a school and when I had a period it cained!!! But the best thing I found for it (when I was a teenager) was swimming, particularly freestyle. It streches out your muscles and ligaments and helps with the nerve pain. Sounds weird but the more active i was the less it hurt.

With this pregnancy I am always trying to keep my back, hips and shoulders inline all the time. I like to cross my legs and sit on one on the couch but am teaching myself not to. crossed legged doesn't hurt me, but try out different positions. And yes a chiropractor would help a lot!

GL