The one in my neck would send pain from up in my head, down my neck to my upper back, over to my right shoulder, down the back of my arm, and then end with tingling and numbness in my fingers. It wasn't to the point yours is, but they had to fix it before they messed with my lower back. I did lose some range of motion with c5-7 getting fused, but the main issue is that I can't look up, down, or lay on my pillow wrong for very long or I end up with a headache (sometimes a migraine).
My lower back sounds more like what you are going through. I was miserable all the time and got no relief from steroid shots unless I just sat around all day on my couch. As soon as I got up and walked around the pain came right back. When that pain was going on (which was most all of the time) I couldn't do anything really. It was an epic battle just to sit on the toilet and try and get up and wipe. Everything hurt from my whole lower back, over to my right side, and down my right leg into my foot (which was numb like you were sitting on it and it was asleep all the time).
The first surgery there was a discectomy. That worked wonders and I woke up feeling almost no pain except from the surgery. It took about a month for my foot numbness to go completely away though. I got through another 8 years before my pains started coming back and we decided to do both the neck and lower back fusions. I don't have the chronic nerve pain all the time now, but only can do most things for a short time before I start having pain that gets progressively worse. So it limits all my activities.
You shouldn't have as much of an issue with yours being in your neck and arm area. The lower back just affects everything you do in life (lifting, bending, twisting, standing, sitting, lying, etc). There is an old thread on here somewhere where I talked about both fusions and the recovery when they happened. If you haven't read it, it might be worth a read. There were other people's experiences with similar issues in it as well. I'll add the link if I find it to this reply.
Here's the link.
https://kentucky.forums.rivals.com/threads/anyone-had-a-spinal-fusion-done.149709/#post-3265407