Thanks for the query.
The pain you are having could be due to compression of the nerve
plexuses at the side where the fetal head presents.
That may not be exactly sciatica
Usually this type of pain will subside after delivery.
You take rest as much as possible preferably in left lateral position.
If you are having excessive pain you can take analgesics for symptomatic relief.
For more details you can ask me through: http://www.healthcaremagic.com/doctors/dr-sree-gouri-sr/63429