Could be a combination of things. Water weight, muscle building, you could be losing weight from different areas then just your stomach (which is the only place most people measure.) etc. etc.
Don't feel bad Tracy. I'm the SAME way, hahaha. But, I mean, at least you're always losing something, so you know you're going in the right direction, right? That's how I try to think about it. It is pretty mind boggling though.