I agree with tagcaver, you are probably adding muscle which weighs more than fat and also your body needs time to adjust. You have had a great start with losing so far. Make sure you are drinking plenty of water, maybe switch to Splenda instead of aspartame for your sweetner. A few more dark leafy greens might be good instead of lettuce go for fresh spinach etc. I didn't check - are you taking a good multi vitamin? Keep up the good work. You are doing great!
Marie