I'm near the end of Jessica Book 2, and I'm going through this same problem. Because I'm writing it during a very specific time in History (Sept/Oct 1781), I have to strictly adhere to what was going on at the time. Up until now it hasn't been too hard. Sure I've tried to be accurate with clothing, food, daily life and speech, but I could pretty much make the characters do what I wanted them to with very little restrictions.
Now though... yikes! I'm freaking myself out! Because very specific historical things are happening and Jessica is a part of them. They are things that are standing in her way, making life more difficult for her.
Let's just say it makes me nervous. So yesterday I sat at the computer wondering where I was going to go, how I was possibly going to work it all out. I was at one of those times when a week has passed in the book but nothing much has happened so you describe it in a few paragraphs. After I got that done, I stared at my word count hoping that I could somehow come up with a measly 300 more words to make it an even 65,000 words. Instead I found myself doing those things I do when I'm not getting those wonderful strokes of genius: staring blankly at the computer screen, messing around with my iTunes list, or getting distracted by Gnomeo and Juliet (see below).
Old lady Red Gnome: "You're illiterate!"
Old Man Blue Gnome: "I'm not illiterate. My parents were married!"
And then somehow, I had it. I had something. And I was writing. And before I knew it, two hours had passed. And I'd written more than 2,000 words. I don't even know how it happened. One moment I was barely slogging through, and the next, I was a super-writer. A genius. I could scream out, "look Ma, I'm a writer!" (I didn't.)
I just love those moments. I know, I know, I'm not really a genius. But it's such a great feeling to suddenly have something there in my brain, something I didn't even know was there before and suddenly it has appeared on the page. It's like magic. It's writing bliss. And it makes me so very, very happy.