Congrats on staying mostly sober, but don't throw yourself a party. I mean this in the best way, having quit smoking. Every time I would quit, I would give myself a huge pat on the back and then I would start smoking again because one won't hurt.
Addiction is weird because your body now knows something foreign and instead of just ignoring it you have to consciously avoid it. It's like you have to develop and constantly flex some muscle not up slouch back into it.
I believe you can keep it up. I bet the TBI has a lot more to do with your sleep at this point than your sobriety. Keep that appointment and I hope you get answers and a plan.