It's called adaptation syndrome.
Your body takes this as a norm. Make a switch for a week or 2 to circuit training or cross training to break through the plateau. You might also bump the calories UP a little for a bit, since your body is likely in famine mode and conserving body fat by slowing down your metabolism. It's a holdover from prehistory when we were hunter-gatherers and more subject to shortages, etc.
I'd really lean toward a period of either short, VERY high intensity circuit training. Look at Periodization of your training as well.
http://exercise.about.com/cs/exercis...begcircuit.htm
http://www.performbetter.com/catalog...fPeriodization
Originally Posted by
TrumpetMurph
Another thing-- Your body will go through phases where it will drop the weight, and plateau for a while, and drop weight, and plateau again. Your body has to play "Catch Up" to your lifestyle changes (I don't know much about all the physiology of it) and my understanding is that basically over time it has learned to function on the 1800 calories/day you're giving it. Keep after it, and the weight will start dropping again. (Any scientific types out there know anything official about this?)