This is not normal, You should still be losing weight. I had the same issue and it was because i was not changing my excersice routine. You need to add a minute a week and change up the routine. You need your heart rate to get higher in order to burn the food that you are eating and if you are not excercising then your body is using the 600 calories you are intaking as fuel and not needing to burn what is already there. make sense?