I've had 3 lumbar surgeries, 2 fusions and a smaller one in between the two fusions. I'd definitely have another if it meant pain would be lessened. But knock on wood, I am pretty much pain-free now...oh, I should add I had my first surgery at age 58 so you don't have to be younger to have good results.
But spine surgery really is a crap shoot in so many ways. First the patient is gambling on the fact that the surgeon she has selected is technically, and diagnostically brilliant.
Then, that the surgeon has indeed figured out which surgery is appropriate for what he thinks is the pain generator...and that he is correct in his decision. More surgeries "fail" because the right thing was not operated on than fail because something went amiss with the surgery itself.
You do not indicate if you have had a recent lumbar MRI. It may be that just by virtue of being fused at L4-5, you have developed an "issue" at the next segment, L5-S1. This would not be at all surprising and it would cause similar issues to what you experienced with L4-L5.
My recent three level fusion was actually a lot less painful than the first fusion I had about 3 years previously. It was a much more complex surgery, involving some spinal reconstruction, and it seems to me, it should have been at least equal in discomfort to the first, but it wasn't. I was off all meds by the 12th day. Now recovery has been longer...but in part that is because I have been VERY conservative in when I start doing things, and everything I have done is designed around not causing a bit of flare to my sciatic nerves.
When you get your neck healed, you can deal with all this. In my opinion, it would definitely be worth checking out. At least then you'd know what you are dealing with and what you might have to face in order to better the situation.