Hi & Welcome to 3FC!
I agree w/the others. If this is a major change to your lifestyle, you could see big losses your first and even your second week. Usually, things should balance out to 1-3 lb loss per week after that. I see you had mentioned "low cal". Please make sure you're eating ENOUGH calories. Never go below 1200 a day. Check out the
http://www.3fatchicks.com/forum/calorie-counters-172/ They have some great tips on making the most of the calories you are consuming. Good luck!