It's really exhausting and progress is extremely slow. It's not a matter of skill or knowledge as I've been doing design, front end, and general programming for 20 years. At first I thought it was because I was on my own, so the workload was tripled, but then realized a major factor is really the cognitive cost of having it all in my mind. The db, the platform, the backend logic, the API, the frontend code, the design, the UX, etc.
Now I try to not work on the whole thing at once. I focus on the backend for a couple of days, then on the front end for a couple of days, etc. This works, but there are many times where something doesn't work as expected and I need to switch between multiple projects (front, API, some other service, etc) during the same hour.
I really don't have a solution to this problem, but I wanted to share my experience. Hopefully someone who has been doing this juggling has some wisdom to share.