I had a similar problem in the past. I did some soul-searching, and realized that the projects that I undertook were huge, and would take at least a month of work in order to "finish." During this time, it was completely unusable up until the very end. Not having anything to show for hard work was demotivational.

The solution for me was to partition my work into hilariously small pieces. When I start a project from scratch, my first few tasks are "create the directory hierarchy," "create a repository," "Hello World," and "create exception-throwing stubs for the basic functionality." The idea is to finish early and finish often. If you can't commit a working version every day or two, you may be working on chunks that are too large.

It'll even sound better to your boss! Instead of saying, "no, I am not done," you can say, "I finished X,Y,Z, and W, and I am having trouble with S and R."