Are you weighing yourself in the morning after you wake up? A 12 pounds fluctuation is abnormal. I fluctuate a lot, sometimes up to 4 pounds from day to day. But there's a pattern to it, and I rarely see more than 2-3 pounds in a day. It's all water of course, you can't really gain 12 pounds over the weekend. But the 175 sounds like major dehydration to me.