Hi Aussie ~ if you didn't have sciatica BEFORE surgery, it seems funny that you'd have it now. The only thing i can think is that it is swollen in there due to the surgery being around that area (L3-4 & L4-5) and just the swelling could be putting pressure on the sciatic nerve.
You should be putting ICE on your back for 20 minutes every 2 hours. This will reduce the inflammation as well as the pain. DO NOT USE HEAT -- this will draw blood to the heated area and increase inflammation and swelling. My Neuro taught me this - and it makes sense.
If your pain does NOT reduce within a reasonable length of time, call your surgeon. You don't want to end up like me -- I have permanent sciatica due to a botched surgery. And ya know what?? IT HURTS!!!!
I wish you the very best ~ PLEASE let us know how you do. God bless & take care. Hugs, Lee