Prepare to abandon ship, if needed. My Galaxy Tales trilogy (Book 1: Into the Mind of God) started out as an autobiography in 2012, morphed into a space opera in 2013, needed to be abandoned halfway through the first draft, finally became semi-logical/readable in v2 (including six months of writer's block where I did nothing but read), got relatively polished in v3, after which I concluded there was no audience for it (too religious for the non-religious and to irreverent for the religious). So, after six years, I shelved it pending a complete rewrite, which will require at least two more drafts that will takes years. I don't mind, however. I learned a lot.
In the meantime, I got inspired to write a fictional trilogy about the Book of Revelation (The Lord of the Earth). This time, I chose my target audience first (primarily Catholics, hopefully some Catholic-curious Christians, and maybe a few thriller readers). I spent a year doing detailed research (much more still to do), didn't do enough plotting (the murder/mystery element fell apart almost immediately), went back to the drawing board, had life intrude for four months with no writing, and am now partially back in the saddle trading reviews and editing early scenes. I'm sufficiently inspired by my current story that I will keep going as soon as I get my life fully reorganized. It will take me at least ten years to write the whole thing. At that pace, Galaxy Tales will probably never get done, which is too bad because some of what I wrote there is very funny, IMO.
I think Temple may be onto something. Try writing short stories and you may find something inspires you to write a new book or finish an existing one. The Lord of the Earth started that way. I wrote a short story called Connor based loosely on the Angel vampire TV series. Many people encouraged me to turn it into a book. Once I started the research, it morphed into a full-blown project, albeit with a completely different plot, setting, and ending.