sparks; Sorry you're having this pain. It sounds like sciatica. It's very painful and usually has to run it's course(sorry to say). Try the suggestions already given. A heating pad might help but don't turn it up too high and accidentally burn yourself-it happens quicker than you think. I've known people that have used medicated rubs on the area too for some comfort. Things like Icy Hot, Mineral Ice, Ben-Gay, etc. You might want to do some internet research on remedies for this. Of course, I'm not a doctor, but that's what it sounds like.
Most of all, take it easy as much as possible. Believe me, this is the easy part. You'll look back on your pregnant days with a smile on your face, in years to come :)
Best of luck in getting some rapid comfort! :)