Second, I plugged your info into the basal metabolic rate calculator at Discovery.com (http://health.discovery.com/tools/ca...sal/basal.html
) and it says your BMR is 2039 calories. Your BMR is the number of calories your body would burn if you just laid around in bed 24 hours a day; it's what you need just to function.
Without figuring in any exercise at all, if you are eating 1800 calories a day, then you have a calorie deficit of 239 calories per day. This comes out to 1673 calories a week. You need to burn 3500 calories to burn a pound of fat, so at a calorie deficit of 1673 per week, you're burning a little under a half pound of fat per week. Six pounds in four weeks is right about on track, then.
I don't know if you should dip much more below 1800 calories a week. On the other hand, I am about 50 lbs. lighter than you and must exercise religiously to see a loss at my current intake of about 1740 calories per day. You might want to look more at upping the frequency and intensity of your exercise, if possible. (But do it slowly, and make sure you're doctor is okay with it first!)
Oh yeah...and drink your water. I guess current wisdom is 64 oz. plus an extra 8 oz. for every 20 lbs. over your ideal weight you are.
I hope I helped a little!