The first question you should ask is, if you can't keep motivated, why are you doing it?

For me, side projects are things I do because I'm interested in them and have free time to invest. If I don't, I don't work on the project, and it's no big deal. Yeah, sometimes I'd love to have more time, but oh well.

It'd be different if I made money off of them, but I don't. To me, that would make it a job, and not a side project.