Just to piggy back on jonr71's comments, women in particular may "stall out" for a couple of days naturally, then get back on track... periodically. It's not indicative of anything you're doing wrong per se, it's just bound to happen every now and then.
jonr71, muscle is technically heavier than fat, since it's mostly protein. You're still right that weight loss will slow if the body is burning muscle as it does so extremely slowly, since it's not an ideal situation and the body tries to preserve as much of itself as possible; furthermore, it's not a terribly efficient metabolic reaction. But from a physical standpoint, 1000 calories of protein weigh 250g, while 1000 calories of fat weigh about 112g.