I have a similar problem. I think I need external motivation, like a job or being a member of a team, to really be motivated to do something. Since I retired early, in my mid 30s, though, I don't have this kind of environment.
When I work alone, just a trickle of productivity comes out, unless I really push myself.
Once, I forced myself to work 4 hours a day for months to push a project out. I was able to accomplish this, but I was quite miserable when I was working.
Before I retired and was working for a company, I was able to push out 10 hours a day including a day on the weekend, and felt fine.
I keep thinking if there was only some way to create a team like environment I'd be able to accomplish a lot more, but I'm not sure how to do that. Reporting my results to others who aren't invested in what I'm doing doesn't seem to work. So, I don't know.