Any possible explanations?

If you are like me, I will gain 10 pounds of muscle before the fat starts to come off! Try taking your measurements once a month!

What types of foods are you eating? Do you eat a lot of pre-packaged or processed foods? Do you drink enough water? Eat enough fibre and healthy fats?

It is highly doubtful that you have gained any muscle as you need a calorie surplus to gain any decent amount and even than it takes time to build even a pound.

Have you started exercising? Your body holds onto water among other things when you begin a new exercise routine to help rebuild everything.

Are you close to your time of the month? That can cause weight gain (not real and normally just water weight)

Most likely it is water retention. Keep doing what you're doing and you will see results if you are following the program. Make sure you eat enough, eat enough fats, protein and fiber and drink enough water.

Also, are you weighing and measuring your foods? Are you paying attention to portion sizes when tracking? Are you using the information in the database? If you are, make sure you check it against the packages of the foods you are eating since some of the items here are not the same contents as what you may be eating. If you make a recipe enter it in the recipe builder to get the most accurate calorie counts... dont' just go off of what the tracker gives you.

Experiement with eating your exercise calories. The site tells you to eat them since exercise isn't accounted for when the site gives you your deficit for weight loss. If you use the calorie burn numbers on this site don't eat back all of them as they are usually higher than what you actually burnt.

LOVE THIS!

We all are going through it, believe me just keep it up. Remember all calories are not created equal. Be mindful of your choices, and chug that water. I have only dropped about 14 pounds in 10 weeks, but lost many inches and clothes sizes.
I struggle too to understand why I haven't lost more and how I can log 50 miles a week and tons of cardio and I gain a pound.

I've been in the same situation. I weighed myself this morning (after my first week of MFP) and - BAM! 168 pounds. This is the heaviest I've ever been. Stick with it. A friend told me that my body is probably trying to figure out what the hell is going on. I'm trying to stay active, eat better and not be a slave to the scale! I feel really good though and my workouts are getting easier so I am noticing a difference there. Just keep on keeping on!

I've just looked at your profile, and 1200 is not recommended for someone who is only 15-20# overweight. The general recommendation for someone in your situation is to aim for a .5-1# loss/week. And if you don't have that exercise figured into your general activity level, then you should definitely be eating those cals.

Give it some time and it will level out.

You mentioned you recently starting exercising a lot more than you used to so your body is most likely retaining water.

Give yourself a rest day now and again (mine is usually the day before i weigh in). You don't have a ton of weight to lose so take it slow and steady.

Also, when you weigh yourself make sure your scale is in the exact same spot (the floor can affec the accuracy - especially carpets). Make sure you weigh yourself the same day, same time, same clothing, same circumstances. Even a glass of water before weighing in will change the results you get. I always weigh in Wed mornings before eating or drinking anything and after using the bathroom.