One thing is you could have gained muscle. It weighs more than fat. What is your body type like? If you are muscular you shouldn't be worried about weight. I know it may not seem like what you want to hear but you're weigh is not an accurate measure of your health.
Also you're diet may not lend to you actually being that much healthier. You should go talk to a nutritionist if you can. They can help make sure what you are eating is giving your body a good balance of all the things you actually need to keep your muscles working which = fat being burned. Check out this link about common myths with dieting.
http://eating.health.com/2008/02/11/...yths-debunked/