If I understand right, you had your hardware out about 11 months ago, right? If the screws were loose, that wouldn't be an issue, since they were then removed. It could be that you have nerve damage, which can take a very long time to heal. I've had two fusions. The first one was in 1977 and a year later they took out the hardware. The fusion surgery went great with no complications, but the hardware removal left me with a numb patch on my back about 4 inches across. It was due to nerve damage during the removal, and it took several years to heal, but it finally did.
Pain management doctors are not all created equal. If you can, I would look into switching to a different one. There are so many pain relief options out there, it's shameful that your doctor isn't providing you with better pain control. I went to a pain management "specialist" who was just horrible and actually ended up doing damage to me! Keep looking until you find the right doctor who will listen to you and give you the help you need.
Some of those people who do the FCE's really are jerks! They think it's their job to prove that you can do more than you're saying and will try to trick you into it. But if you're honestly trying to do your best and cooperate, boy can that backfire! Are you now on disability? I'm so sorry you're having to deal with all this at such a young age. I hope you're finding ways to fill your days productively, even though you can't work. I'm older than you, 51, but I had to stop working 7 years ago and I really miss it. I loved my work!
But to everything there is a season.
Hang in there,