I went on a trip for 10 days. This trip was not a relaxing vacation. We were swimming, hiking, kayaking, and walking around a ton. When I got home, I weighed myself and to my delight I lost about 2 pounds. I have been home for about a week now and I already gained one of those pounds back. I have been counting calories since getting back and I know I have not eaten 3500 extra calories in the past week. I have maybe eaten 500 calories extra this week. The weight loss is not water weight because my measurements were also lower when I got home (I lost about half an inch in my waist and half an inch in my hips) and I am not on my period.

I know its just a pound and I shouldn't be worrying about it but, I don't understand where the extra weight came from. I am afraid I am going to keep having unexplained weight gains. I feel like my body has a set weight where it wants to be and if I ever dip below that amount, my body will automatically bring my weight back up.

The weight that you might have lost might have been water weight. With all the activity you did, you may not have been hydrating enough. When you got home, you started back on what worked for you and since you're no longer dehydrated, your body went up a single pound (just water hanging out fueling your organs and your systems) and that's also why your measurements were down -- with less water in your body, your body measurements go down too.

Your body may seem like it wants to stay at one weight and it will sabotage you by holding on to it. I often think my body feels that way too! But that's not what's going on.

Your body will respond to lower calories, in general (without metabolic issues, and I have them!) to lose weight. But it also responds to water and exercise and injury and disease (in other words, water will affect your weight when your body is swollen from too much exercise or if you're sick, and so on).

The issue is not that one pound that you've gained, but rather the five or ten that come after that one pound. You can't let that happen -- that's not water weight!

Secondly, while I don't have proof of this in any scientific manner, I think my body (at least) does get nervous when it loses weight and I have to "calm" it and tell it that it's okay to lose the weight, I'm not in the middle of a famine. As it gets comfortable at that lower weight (what others might see as a plateau), it'll eventually feel comfortable to go down another pound or two.

For me, it's slow progress. Let's hope that for you, it's just a blip in the road.

I agree with everything Rana says, but especially what I bolded. I think once it realizes "oh it's okay to weight X amount," then it releases more weight. That's been my experience. And I always weigh less (by 2-3 pounds) by not exercising; however, my aches and pains come back and I'm sure eventually I'd look fluffier so I'll just take the few pounds.

It can still be water weight, especially if the measurement change includes the waist. How are your sodium levels this week?