Maybe you want yourself to be interested in this particular project, but you might really not be interested in it. Sometimes you can't force interest, and it's often tough to focus when you aren't interested. I've felt what you're feeling before. I realized that my problem was that I just was not into the project - I just could not bring myself to focus on coding because I didn't really want to. This is fine though. As an adult, hey, sometimes you don't have to do things you don't want to do. You can have ice cream and beer for dinner; you can pick some other side project, or nothing, to spend your time on.