WHY SO HARD

I've just published the 4th Paranormal Washington novel, Deadly Encounters. The fifth is the last book in the series, working title Toxic Bliss. But before all that jazz, I was hoping to write a couple short stories. The first short story is called The Artist; a dark...IDK, let's call it a thriller. I'm not entirely sure what genre it would fall under. It's about a woman falling in love with a serial killer. The second book is yet undecided between three books I have started already:

Cana: about a cannibalistic whore.

Styx: about a gargoyle living in Hades during a rebellion against the statues quo.

And the last one, actually a spin off from the Paranormal Washington series, a collection of side stories about some of the character's adventures between the books. These short stories would answer some questions for the readers, questions like:

• What exactly did Nil do in Canada? He left Washington State a suicidal self hating fella, and came back as a man on a mission. I think people might be interested in seeing that transition. 
• Raina mentions a few times how often Alistair had saved her life while she was on the job, and I'm fairly sure people would LOVE to actually read some of these adventures.
• How did Katie become a Hunter? When we left her at the end of the 3rd book, Grave Omen, she had the desire but Raina was the only one who believed in her. But, with Raina dead, how did she prove herself to the powers that be?

All of this I should be planning, and yet...and yet I can't stop thinking about the 5th and final book, Toxic Bliss. It really wants to be written. It's alive in my head! Why is it so hard for me to stop writing Paranormal Washington and switch gears...Of course the the compilation of short stories for Paranormal Washington  is kind of cheating on the whole, let me write something else for a change...thing