Chimel, from reading your posts, I'm sure you're smart so I imagine you've studied this more thoroughly than I, but I cannot imagine 600 calories per day being healthy for any person who weighs 200 pounds, regardless of their height, age or activity level. I hope you're being safe. I wonder if your metabolism has entered into some sort of starvation mode where it is protecting itself as much as possible.

I am relatively young, weigh 213 pounds and eat around 1700-2000 calories per day and I have been losing 0.09 pounds per day on average over the last 102 days. I don't exercise and I don't work particularly hard although I do put a fair number of hours in. I've studied the formulas you're talking about and my actual weight loss vs calorie consumption works out fairly close to what the formulas predict.

I guess I would suggest that you consult a Dr. before spending a lot more time at 600 calories per day. Most places recommend no less than 1200 calories per day for any adult, much less an adult who weighs 200+ pounds. Stay safe and healthy, and congratulations on losing so much so far.