When I had the Mirena, my symptoms were pretty much constant. I battled yeast infections for the first three years of having it in, and then it turned out that not only was I suffering from yeast infections, but also from vaginal dryness that got so severe, I often couldn't sit still because of the irritation and itching, and I was waking in the middle of the night scratching myself. I certainly couldn't have sex with my partner! I had my Mirena removed nearly eight months ago, and I've just about got rid of the last of the dryness. Every now and again I will have a couple of days where mild itchiness suddenly appears out of nowhere.
So it could very well be vaginal dryness if you don't have any abnormal discharge.