Have any of you tried seeing a massage therapist? (not just for a spa-style swedish massage, but an actual deep tissue specialist?) concentrated massage to the surrounding tissue can often loosen the area enough to give your sciatic nerve some space if it is being pinched.
Pregnancy can cause a change in the tilt of your pelvis which can cause severe pain in some women... usually stretching and massage can help to reduce that pain.

*helpful hint for low-back pain/tension:*

Lie on your back with your arms crossed on your chest as if you were going to do a sit-up.
Have some stand above you with their hands on your arms, pinning you to the floor.
For 15 seconds, try as hard as you can to do a sit-up while they are holding you down
Relax for 10 seconds
Then repeat.

By isolating your abdominal muscles you will allow the muscles in your lower back (specifically your quadratus lumborum) to relax.

This is more of a quick-fix and its effects will wear off after a short amount of time, but at least its something!