I think longroad has some good ideas that you should check out.
As far as reading facial expressions, some people are really good at it. Our faces can betray our thoughts and emotions. Can someone be wrong? Sure. But what if they aren't?
In my case, it was my voice. For almost two years my voice had no inflection when I talked to her. She could hear the difference when I talked with others, like the kids or co-workers. It was a defense mechanism I was using to try to protect myself, yet I didn't realize it until she pointed it out to me.
I generally believe that at some point in a relationship, your SO is going to know you better than you know yourself. There are exceptions, but really, that is part of what a M becomes. Once you both are actively working on things, there comes an understanding of the other that sometimes that other person doesn't seem to notice except when it's pointed out by someone other than yourself. Does that make sense? I'm confusing myself...
Anyway, if you think your BW is misreading your facial expressions, then what can you do to change that? Is it her fault for the misread? or is it up to you to find a way to stay engaged, or let her know that you need a mental/emotional break or even just a nap to re-energize?