It sounds to me like you're a victim of the "Domino Effect." It seems to happen most of the time after spinal surgery. AFter the surgery, the levels above and/or below will fail due to taking on more of the load.

Unfortunately doctors don't tell their patients that this will happen. They should, cause it causes more surgery -- much to their delight.
I've had 3 spinal surgeries, and if it were me, I'd never had another unless I was in danger of permanent nerve damage or my spinal cord was being impinged. Trouble is, you say you have bilateral sciatic pain so I must assume that your sciatic nerve is being impinged. I have permanent sciatic nerve damage, and it's NO picnic!

How long has your pain been going on? Because nerve damage becomes permanent after about 18 months!
I hope you will get other opinions. Before undergoing ANY spinal surgery you should get at LEAST 2 other opinions from NeuroSURGEONS and find out what they think. Don't just go with what one doctor thinks. that's a big mistake!
Let us know what happens, will you? I'd be interested in finding out what the end result is. God bless and please take care. Hugs, Lee