Stalled

For the past 10 days, I have only lost 1.5 lbs which is really frustrating since the month before, I was losing 4 lbs a week.  I wonder what stalls my weight loss.  Is it the diet sodas? I don't think so.  I have a large cup at least every other day before.  Is it the meals not being spread out equally?  Is it the exercise (I noticed that everytime I run, my scale won't budge for 3 days ... but I still chalk this up to coincidence since I don't run too long and I only lose about 150 calories so I don't think I'm entering starvation mode)?  Is it lack of water?  Is it too much salt?  What is it?  I seriously wish I knew.

The scale finally moved today.   Yesterday, I had two shakes, 2 bars, scrambled eggs and tilapia with butter, lemon, capers, spinach and tomatoes.  I ate my lean meal at lunch instead of my usual dinner.  Did this make a difference?