But to answer your question about the source of my drive:
Firstly, I don't think that my commercial commissions are satisfying enough in terms of creativity. They are often rushed, with hectic deadlines, and require a lot of mediocre design work. I cannot complain but I would easily get burnt off if not for my personal projects. It's also not that long since I decided I would like to focus totally on arch-viz and I just need to craft my career a bit into that direction since my client base is at the moment pretty random, spanning from vfx industry to advertisement.
Secondly, I have some constantly insatiate hunger for it. I get inspired a lot on a daily basis and my head is crowded with unrealized ideas. Making them come to life is still one of my biggest joys. I have also this kind of affliction that makes me really positive about the stuff I am currently working on and really negative as soon as it's finished. It may not sound that great but it really pushes me forward.
On the other hand, I am pretty impatient and try to work smart and fast. I buy, re-use, adapt, fake as much as possible, which is not my preference at all but I have learned to accept it. I look with some hints of envy at artists that create their intricate works entirely with their own hands in every crazy detail.
I must also admit in the end that I probably just work too much and it'd be much healthier if I did less. : )
I gotta say that I can identify with all this very well. I personally havent really found a solution for me yet. I do have the same problems you descibe which often leave me exhausted and lacking the drive to do more.
Finding the balance between perfectionism and speed is another problem. Its also not what i want but I figuered latley that I have to accept it.
What I actually wanted to say is, you kind of hit the sweet spot in all this crazy complexity. Thats really something to be proud of. Well done once again!