Me too - I have to write my thesis this year.
A program that really helps is called "Write or Die". There is a free website version of it. Basically it is a simple typing space where you choose how many words and time you need to write and then you're typing and if you stop too long (you can choose if it's really fast or it gives u long time) it makes the screen red and makes bad noises (you can choose alarm clocks, baby crying, violin poorly played) so it gives a punishment (and because sensory overload, particularly so) if you don't write!
There is a paid version too, though it's quite expensive $20, so I avoided it but I saved up and bought it - yesterday actually. And that works even better because in addition to the bad noise, it puts a big scary spider onto the screen so now I write much more to avoid seeing it (cause you can make it full screen and "always in front" so you can't just alt tab out of it).
If that is too harsh, there's also incentive mode that plays kitten purring sounds or other nice things of your choice each time you type a certain ammount of words.
It is the only thing that worked on me so far, I have been putting off four days writing it and now because of that program I at least have 1300 words so it's a useful kick to get you started.
All the conventional suggestions like Pomodoro Technique, chunking it (I've read even just do 10 words every day so that it's low enough u definitely do it) just didn't work for me - but then again aside from Asperger's I have severe depression so my motivation is exceptionally low.