That's awesome!!! :D It could be water loss... if you've been drinking a lot more water, a lot of times the body stops retaining it because it realizes you're providing it now. Also, if you've been working out regularly, you're gaining muscle, which of course weighs more. So, if you've been gaining muscle but staying the same weight, you're losing fat or water or both. Either way, that's FANTASTIC! Enjoy! :D