From skwigg's journal:
Part of a conversation I had about scale weight and trusting your body:
Just know that your body is trying to help you. It wants to maintain a stable weight in a healthy, comfortable range. It's so good at that that it will do it even if the person is oblivious. Think, normal-weight, non-exercising, non-tracking, non-dieting husbands. If they exercise more and eat less, they don't necessarily lose weight because their metabolisms get thrifty and conservative in reaction to such things. If they eat more and don't move much, they don't necessarily gain because metabolism will increase in response to the extra food. That's why calorie math never works out as expected. Your body is constantly adjusting for "stable and healthy" even if you decide to go on a lettuce and dandelions diet, or live on Big Gulps and chili cheese fries. It does what it can to maintain a healthy weight, even and especially if we're being restrictive or reckless.
Also remember that your body naturally fluctuates by several pounds a day due to water, sodium, glycogen, hormones, humidity, poop, etc. You may be trying to assign meaning to a random fluctuation that is not a reflection of your eating/weight/workouts.