OK, I've talked about this before, but as I'm experiencing the phenomenon right now, it's worth going over the ground again. What do you do when the novel turns into hard slog?
The natural inclination is to throw oneself to the carpet and drum heels screaming all the while. That's what's going on inside, isn't it? But unlike Lady Caroline Lamb, we refrain from such demonstrations and instead carp and grumble at loved ones. At least, that's what I find myself doing.
Believe me, it doesn't help. So what does. First off, contact your writing buddies and scream argghhh at them. That's what they're there for and they will commiserate. They may also have some useful pointers. Then it's time to look at what's really going on here.
Assuming there are no external crises holding your attention, there's got to be something wrong with the story. Is it characters behaving out of character? Have you gone off at a tangent and can't get back? Is the scenario just plain boring? Let's face it, if it bores you, it's going to bore the hell off the reader.
The commonest thing I discover is that I've lost the impetus of action. Too much exposition, not enough go. In my current book, the sleuth isn't physically close enough to the action, so I keep finding her slipping out of it. The moment I get her back there, everything takes off again. So this is one to watch.
But the plain truth of the matter is, some books are like that. They don't flow well, it's all stop/start and you honestly do feel like you are wading through treacle most of the time. There really is only one solution, I'm sorry to have to tell you. Keep going.
Bite the bullet and push through. Write one sentence after another and just suffer on through it. Get to that finished first draft. Tell yourself you can fix anything in edit mode. Drink gallons of tea, stuff yourself with chocolate or whatever tickles your comfort zone, take frequent breaks. But write, write, write.
The payoff? At worst, you've got that draft and you can work it. Much more likely, it won't be nearly as bad as you think. Several of my treacle books have turned out to be among the best I've written, according to report and feedback.
The point is, just because you're finding it difficult doesn't mean your craft and talent is any worse. You still know how to write. You still write at the level you write. The reader ain't going to know whether you raced through like a demon enjoying every minute, or you went through hell and high water cursing the day you decided to be a writer.
Ergo, it doesn't matter. It matters to you at the time. I'm about to slit my wrists at the moment, I can tell you! But I know from past experience that I'll get through it and I'll have a complete book, and I'll be able to edit it into shape. Treacle? Bring it on, I can handle it.