I read somewhere, that if you are exercising you should not go below 1200 calories because it can affect your mood among other things.
It is tempting to go as low as you can to loos as fast as possible, but you want to do this for life, so what's the rush...
Also, along with what some others have said, just because the scale doesn't show it, doesn't mean you are not loosing. If you are building muscle, then you might be losing fat, but because the muscle you are replacing it with is heavier than the same amount of fat, the scale may not reflect it, However, muscle takes up less space than fat, thus the drop in clothing size without much lbs lost.
My body mass index is actually rather high compared to others of the same size and and hight, but they don't work out and so I have more weight because of more muscle mass.
My advice is to ditch the scales alltogether, that's what I have done and I have never looked back. You are a much better judge of your progress by how you feel and look than how much you weigh.
Hang in there and don't give up! You are doing great!
Cendrine