1 week on plan and gaining?

Unless you burned 21,000 calories in your first week, what you lost was mostly water weight, not fat. My first week I lost "4 lbs" and the next week I "gained back" 3. I'm happy I at least lost something. It takes time. Slowly but surely, if you stick to this, you will reach your goal. Don't get discouraged :drinker:

Edit: Sorry, I forgot to add that a pound equals 3,500 calories. So to lose a pound a week, you have to burn or have a deficit of 3,500 calories in a week. 3,500 x 6lbs = 21,000 calories.

My assumption is that either you're weighing at different times of the day or that you were still carrying some extra weight from the previous night's meal

It's generally considered ideal to do your weighing in the morning after going to the bathroom and before eating/drinking anything, simply because this will probably be your lowest weight in the day. People typically gain several lbs through the day from drinking and eating.

Some fluctuation just happens though, I wouldn't get too worried if you have little wiggles in your weight over time, the important thing is the overall trendline. If you gain one week that's alright, just as long as you're not gaining, and gaining, and gaining(while trying to lose). If that happens then you know you need to reevaluate your methods or your plan.

You're probably getting too much sodium in your diet, and that's causing you to retain water which is leading to the fluctuations in your weight. Do not think of MFP as some quick fast way to drop a few pounds. Dropping six pounds in a week is impossible and impracticable. The human body sometimes will shed a lot of water at the beginning of any type of diet change, but things will normalize within a few days. Just keep logging in your calories, doing a little exercise, and you'll lose all the weight you want to lose. Buy a food scale to make sure you're eating the right portion sizes. That's a big killer for a lot of people.