Certainly does sound like the sciatic nerve.

Great advice Arimeh! I would have suggested just that.

I recommend tennis balls, you can lie on tennis balls, one under each butt cheek and roll around to find the sore points. This will massage the muscle in the butt which is often responsible for the pain you have described (the piriformis muscle). (The sciatic nerve basically runs from the spine, through your glutes (Butt muscles) and then down your leg. The doozy is that it actually runs through the middle of the pirifirmis muscles in the butt and when this muscle gets tight it can pinch the nerve which causes the pain. Pain in the area of the muscle tightness and in the area the sciatic nerve innervates. The changing shape of your body in pregnancy and the shifts in your pelvis and back can aggravate this muscle.

So - stretch that glut as Arimeh suggested, massage it as much as you can bear and the sleep position advice is great.
3) When sleeping, try to sleep on your side with a pillow between your legs so it brings your back into line with your hips, instead of rolling forwards.
It is the hips out of line which really irritates this muscle.

I really appreciate understanding what is going on visually when I am in pain and if this helps you too you can google "piriformis syndrome pregnancy" (or other variations such as sciatic) to get some more info and if you do a google image search you can see exactly what is going on.