You might want to seek out solutions that have nothing to do with game making. Any activity requires some sort of focus, so it should be a general problem, and I would assume what helps someone to express art in a hobby with conditions such as yours, would maybe help in creating a computer game as well.
For computer stuff and a game project you can of course use time tested approach that anyone could and should use, regardless of any conditions: Divide and Conquer. Break down the project into smaller chunks. Finishing them should motivate you. And you know your own limits, so do not hesitate to break down small chunks into even smaller chunks.