I get stressed out over money. I suspect a lot of us here don't have or want "normal" office jobs. I do think being self-employed is less stressful in many ways, but it is also very feast or famine in terms of income so I worry about that a lot.
The other thing I get very stressed about is my ability to get NDT. I will be dependent on thyroid for the rest of my life and I've had so many struggles with doctors not wanting to give me enough of it that there is always worry in the back of my mind about not having my medication.
I don't really know how to get around these problems!
As for lack of motivation... I think those feelings are very common with writing. I'm a huge procrastinator when I don't want to do something. I have to shut myself off from the world, no music, no internet, no people, nothing, and drink a ton of caffeine in order to focus. I don't know how long it takes to write a thesis but usually I will power through whatever I have to write for as long as it takes - working every day for 2, 3 days, whatever - to get it done instead of trying to do it in little chunks over several weeks. Also, my brain is better in the mornings - by mid afternoon I'm not as sharp.
Then again, what is the worst thing that could happen if you just decided not to do it? If there is no point at all to your life as it is now, maybe you just need to see it as a sunk cost and invest your time/energy into something you are actually interested in and which would be useful for your future.