Ice on the Inside?

The last handful of times that I have gotten in my car, I have had to scrape ice off the inside of the windshield. And not a little of it either. Not being able to remember this happening before, I started thinking about air or moisture leaks around the windshield and other worrying things. Then it dawned on me: I leave the gym every day a sweaty mess, and drive home--filling the car with moisture, which then freezes overnight. Great, just great.