If your BMR is 1400/day (which seems reasonable if you are a woman of average height) and you are not sitting around all day, you probably burn 1800+ calories per day BEFORE exercise, just from regular moving around.  If you run 4 miles above that and you're burning approx. 100 calories per mile, you're expending something around 2200 calories per day. 

However, I disagree with the first responder who said you're not eating enough. If you haven't lost weight, you're probably eating more than you think. It's probably easier to eat low-cal on low-carb diets, which is why you've lost weight on that method before and also why you've felt weak on runs while going low-carb (because you're eating far fewer calories, not enough to fuel runs). If you're really eating 1500 calories per day, EVERY day, you would have lost weight, at least a couple of pounds, by now.

So, first, look at how well you're really measuring your food. Most people don't do a great job of it, particularly if they eat foods which are not pre-packaged with nutritional information. There may also be other confounding problems. With a deficit of 500 calories a day (if that's correct), you will have lost about 4 pounds by now. However, if you have a high salt diet you could easily retain a couple pounds of liquid. If you're a woman, you may have simply started your diet when you were at your lowest weight in your cycle and now you're at your highest weight of your cycle, so you might see a dramatic loss in the next week or two as a result (this happens to me often). Another possibility is that when you started dieting you also started moving a lot less outside of formal exercise without even realizing it. That is your body trying to conserve a little energy, perhaps by fidgeting less, making you a little lazier about where you park your car, whether you take the stairs, etc. You have to recognize that impulse in order to fight it.

My last suggestion would be to reevaluate how you are weighing yourself.  I do think the scale is extremely useful and that it will show fat loss.  However, you have to weigh yourself in a productive way.  Weigh yourself daily, at the same time, wearing the same clothes (or better, no clothes).  Write the weight down.  At the end of each week, take the average of all seven weights, this is your weekly weight.  Hopefully doing it this way balances out the days when you're retaining water or you ate a little more for dinner the night before or you're a little dehydrated and gives you a more meaningful measurement.  Do this for at least a couple of months before evaluating how your diet is working - one month is not long enough to get despondent).  You may find there is a downward trend, even though the daily weights seem random and not hopeful.  If you're maintaining your weight (on purpose), you can average weights over a whole month to make sure your weight isn't creeping up slightly from month to month.

Hi I know this thread is old but I hope your still around. I didn't read all

of the other responses but here's my $.02.

You say that your caloric intake has been the same over the past month, your

trying to lose weight which I may be wrong, means your most likely a beginner.

If you begin any new physical exercises, your muscles will begin to grow. As

you know muscle weighs more than fat. So gauging your success based on what the

scale says isn't always the best option. If I were you I would go to GNC and

pick up a set of calipers. They measure body fat instead of weight.

As I've said this was posted a month ago so IDK what you decided to do but I

would keep on the same path, buy some calipers. Or if you want an easier BF

estimation get a nice scale that uses BF impendence testing. It isn't as

accurate as other methods but used week to week it will be consistent in

telling you if you have gained or lost BF. I usually get discouraged when this

sort of thing happens to me but I have to remind myself that this kind of thing

happens.

and to the idea I saw that said low carb weight loss

was due to the fact that it is easier to take in fewer calories... well yes

kind of. While 1 carb contains 4 calories a single gram of fat contains 9. And

protein 4 as well. The body burns calories in order. First, you guessed it

CARBS. 2nd in line are fats and third down the list is protein. So if you take

in very few carbs then your body will use the fat you consume firstly. Your

most likely taking high amounts of it. While your body is metabolizing that fat

its using the protein in one of the hundreds of ways, my favorite energy source

can be used. So it feeds on your fat after there is nothing left. If your

hungry and you eat more then the process starts over. Which is why low carbing

works. Not because you eat fewer calories. You could actually eat more and

still lose weight. taking away the first  energy source and allowing it to

feed on the fat you take in its cutting out a step leading to weight loss. You

can do the same thing with fats, its easier to lose weight but much, much

harder to low fat diet. Your only meat options include chicken breast and fish.

And you need your protein.