I have to agree with potatofree. If it's been hot where you live and you've been active and sweating, then this may be the cause. For example, I went to Cedar Point amusement park last week and the weather was 98 degrees. I drank AT LEAST 200 oz of water that day and only peed once. It was just being naturally sweated out. Sit down and try to think of any differences lately (higher activity, added carbs, more salt, hot temp, etc...). If nothing explains it, then get to your doc right away.

~Angi~