I agree about getting your thyroid, vitamin B, vitamin D all checked, etc.
And tell your pdoc to address whether it might be a side effect.
But, in my experience, this sounds like depression setting in. To fight it, I try to to "engrossing" things that require little effort, only enjoyment, like: watch my two favorite movies: Muppets Treasure Island, and Shrek. (and this time of year, I watch Muppets Christmas Carol); go for walks--with the dogs, who don't require conversation; scan MSN news on my homepage....look at recipes in cookbooks (but I avoid actually cooking because I can't keep track of the recipe items or steps, grrr); stuff like that.