I have suffered with this for as long as i can remember (to the point that I literally couldn't walk xmas 2011 because it went). I has it right through my pg with dd2.
It didn't affect my labour of birth. Try as much as you can to stretch it out (i can show you some if you like one night). That really helped me. As did warm baths/hot wheat bags (Last thing you want to do in the heat!)

I still get sciatica pain on and off but if you can continue to stretch it out it doesn't last as long or as horrible.
Give me a call if you want me to show you anything. xx