Hi Mary,
It's hard to answer this specifically without seeing the painting, but I can give some general feelings on the subject. If you want a specific answer you need to post the image and details of the area in question.
First of all, if you are working on a canvas with tooth, sanding will create a very different surface. If you're painting on a panel you can sand. Many artists working on panels regularly sand between layers, assuming the under layer is dry.
But I think your query calls to mind another type of answer. Today there is a big emphasis on attaining a more painterly finish, so in that case, there is an illogical fear of refinement. I feel, a lot of people have been brainwashed into thinking this is the only way to approach painting. The notion that art erupts onto a canvas is a romantic fantasy that informs our idea of the way artists are supposed to be. In my opinion, the majority of "painterly" artists have made refinement a bad thing because they are incapable of achieving refinement without sucking the life.out of the end result.
I tell my students that you can't overwork a painting, as long as you know the end you are trying to achieve. In your case it sounds like you were trying to work things out as you painted. Never a good idea! Things need to be resolved first, before attempting a finish. That's what studies are for. Time management guru Steven Covey says, "Begin with the end in mind."
Certain master artists achieve different degrees of finish throughout a singular painting. Someone like Bouguereau juxtaposes very fine finish in the head against a looser background. Various elements in the painting fall between the two extremes based on their importance in the overall hierarchy. This was all the result of great forethought. Bouguereau, arguably the most successful artist of his time, did extensive studies for every single painting he did throughout his long and storied career.
My advice would be to consider what you've done as a very involved dress rehearsal and start anew. I guarantee the next version will go faster and more smoothly.
I scrapped a painting after three months of work. It was on a previously untried brand of canvas, with a brand of paint I had never used either. The longer I worked on it, the more I hated the way it was coming out. Finally, my dissatisfaction trumped my justification regarding the amount of work I had invested. Here is how it came out on the second go around:
http://forum.portraitartist.com/showthread.php?t=3553 In the end I'm so hoppy I tossed the first one.