I don't think there's a lot you can do, my mum has it and is on tabs that treat labour pain and my grandad also has it and went in to have an epidural last week.
It might sound odd but you should get some relief by lying on the floor on your stomach and drawing the affected leg up. It seems to ease the pressure on the nerve. Other than that - ibuprofen.
Sciatica pain is caused by a trapped sciatic nerve, and can have several different causes. If it's severe and has lasted for 6 months your GP may suggest an xray of your lumbar spine to rule out various causes. Exercises from a physio , pain killers , and getting the balance between rest and exercise right.