Well, several things are. First, you're shrinking! Congratulations. Obviously you're losing fat. You may be partially replacing that with muscle, you may be retaining water if it's before your cycle, it can be a lot of things.

Also, there is what's known as "the dreaded 3 week stall". Real common, don't worry about it. If you're losing inches, you're fine. You can also check your ketones if you're really worried.

If you're sticking to your plan, watcing salt and calories (not gorging or starving) just keep going. Put your scale away and promise yourself you're going to do this another 3 weeks and see what happens.

Great job so far!