First drafts are always crap, don't let that discourage you.
Some writers like to outline (thoroughly) a story to the end before writing the first scene (and when they do write the story down, they don't even have to do it chronologically, because that's how well they outline plot and chapter beforehand). Others like to plunge right in with only a fuzzy idea of who their main character is and one inciting incident / object / setting, whatever. They like to discover their characters and plot while writing. When they found their them, yes, they will have to go back to the beginning and add a few (OK, a LOT) of clarifications. There's nothing wrong with either method. The writer automatically chooses the method that works best for him.
As I'm of the latter type, I have to
- revise the beginning. Does the story goal expressed in my first-draft beginning have anything to do with the finale? Turns out, in my first draft the story goal wasn't expressed until 2/3 through! I had to move it up front. It changed a lot, but not as much as you might think. Yes, the characters suddenly knew things in chapter one that before they learned only very much later, but most of the action still worked.
- go over each scene and revise for scene goal (does the scene have a scene goal that moves the plot forward toward the finale? If not, revise until it does) and focus within each scene (does the scene stay on topic regarding the scene goal).
- revise for theme. Does every scene aid toward the novel's theme?
- revise for character. You know your characters pretty well by know (better, imho, that from an outline.) You've found his voice, completed his character arc. You know how he was and how the story changed him. Now make his voice and personality consistent throughout.
Pacing, clarity, coherance, consistency -- the time to work on these things is once you've finished your first draft. First draft is where you jot the plot down in a hurry and sketch/get to know your characters. Also, I find that it helps me to reread my favorite how-to's on creative writing before I revise to remind me off what pitfalls and issues I have to look out for during revision, and to get into the mood.
So don't worry about those vague/forced scenes right now. Finish the novel. Take a break. Then revise. Or workshop your novel.
There is one exception in my experience, where the just-push-on technique doesn't work, that is when I have maneuvered myself into a corner, for example my characters into a situation that I don't see any way to get them out off. "I have a plot problem" has become a well-known explanation amongst my friends and family for any lingering foul mood on my part. At least twice I found that my premise/a crucial point of magical system contradicted a later development, so that the whole trilogy (work of oh, 8 years) seemed to be about to collapse. No matter how much I started at the screen, there was no solution to be found. It took me two full months away from the screen (with lots of mulling over the problem with help of pen and paper and a lot of going back to the drawing table) until I found a solution. Some things can't be forced. (But most things in a novel can be made to look plausible in the end ;o)
Anyway, best of luck!
P.S.
"a lot of stress and hard, painful, tedious work ..."
In my opinion, that's pretty much what writing is.
I second that. Many people tell me that if I fail to get published (after trying for many years) that I could just go on writing as a hobby, "to express myself" or "release my creative energy" as if it where some sort of refreshing psycho therapy. It's the opposite. It's stressful. It's draining. Painful. It's alternately exhilarating ("I just had a great idea!") and causing deepest depression ("I have a plot problem!") It's a permanent emotional rollercoaster ride.
