Theres to exercises you can do actually one is to sit at the end of a chair and put your right foot/ankle on top of your left knee. Then lean forward and hold for 5 seconds, make sure your belly had enough room between your legs and end of the chair dont want to squish baby. you should feel a little stretch under your right thigh and hip. repeat with the other leg as well. My favorite exercise would be to lay on the floor on your back flat. bring your knees up and together bent. dont lift back or feet or head of ground just keep flat with knees bent. Then gently rock your knees from side to side. it should relieve your spine and pelvic area.. do this a couple times during the day helps alot! hope these help..
Sciatic nerve pain can be awful. I have it all the time. There isn't much you can do in pregnancy. Maybe some physical therapy along with heating pad and tummy support would probably be best. You could also look into pregnancy massage but only have it done by someone licensed and who treats expecting moms. Some massages are not recommended during pregnancy. It will help loosen things up and hopefully release the pressure on your nerve which is causing you so much pain.
Let me know if you find anything! Nothing has worked for me so far, and luckily I'll be having my baby girl in 2 days so I don't have too much longer. Tylenol, heating pads, warm baths help, and getting a belly support may help to take some of the pressure off, that's about all I've found for temporary relief :(