I have had sciatica with both my previous pregnancies. It was much worse with my second, and actually made me wonder whether I can survive a third pregnancy.
I went to a private physio, who was a miracle worker. She did a combination of massage and acupuncture and she got me from a point of barely being able to walk, to feeling almost normal.
If you have it, ICE the area, do not use heat. The ice brings any swelling of the nerve down, and heat makes the nerve inflamed, which causes more pain in the long run.
Another massage trick my physio told me about was getting your other half to use a ball and run it over the area, firmly, as a massage.