I had for the entire second tri and the first few weeks of the third. I told my midwife i was going to cut my leg off if she didnt fix it
I made a thread about it at the time, trying to find it for you but doesnt help that i spelt sciatica wrong in the title...
I think the advice i was given by everyone was basically the same:
1) see your osteopath (if not an osteo then try physio)
2) go swimming.
I didnt see an osteo but i went swimming a few times and oh my gosh its amazing how much instant relief you can get.
If you can't get in a pool, getting in a bath worked for me, give that a whirl.
A lot of people say that there is no cure until the baby comes out - i hope that isnt really true!
In the end i didnt find any 'magic cure' for it, but it DID go away and that was the best day of my life. Hope yours does too