Exert your talents, and distinguish yourself, and don't think of retiring from the world,
until the world will be sorry that you retire. - Samuel Johnson
You've been pushing yourself hard for over two weeks now. Even if you feel you could have done more, you have made the time to write more than you usually would - and that can be really, really tiring.
I've seen it a lot during NaNo - it's happened to me during NaNo - the mid-month slump. There's such a long way to go, you're never going to get there and you're tired.
The best advice I can give you is this: don't stop writing. Don't take a few days off. It's like sitting down after a day of cleaning when you've still got more to go. It's doubly hard to get back up again and keep going.
Picture the goal. Take a couple of hours to have a bath, watch a movie, maybe even see some of those people you live with whose names you're starting to have trouble remembering. But then get some words on the page - even if it's only a couple of hundred, or a hundred, or twenty-five.
It's only two weeks to go! You can do it!