I am as well guilty of starting many side projects and working on them in parallel (about 20 currently). I tried various approaches of "managing myself" in order to get some progress on all of them. I tried to limit the number of projects drastically and also to a single one. That did not really work, because my heart was always drawn to these other projects that I had discarded. So currently I have these 20 projects and try to keep track of all of them. I choose one from day to day and try to work on it. And so far this approach works quite well.

I think it boils down to weither you keep track of all your projects (what's to be done next), that you do not try to plan ahead too much and that you do not plan too many tasks for a single day. If you stick to these guidelines there is a high probability that you get a good experience ("did that, finished that") every now and then which keeps you going.