I went through a seeming "plateau" recently, which is why I joined here for some support to get me through it. The first week, I gained 1 lb, and the second week I gained 2 more! I didn't know what was going on.
Indications said it might be muscle gain, but I wasn't making any gains in strength, and I just wanted the approval of the scale. So I did some dietary analysis and realized I wasn't eating enough protein, fat, or calories. That, and I needed to start mixing exercise stuff up again.
I tweaked my diet to include more protein, more (good) fat via flax-seed-oil, and after my analysis, I realized too many of my carbs were coming from sugar. I'm not an Atkin's dietter, or low-carb dietter, but I saw a trend that disagreed with me, so I've changed it and now try to make sure my sugar intake isn't ridiculous. I've actively tried to cut sodium back, too.
This time, back on the scale, it says I lost 9 lbs in a week - which I find highly unlikely, but it would keep me "on track" if I didn't take the other two weeks to heart... (i.e. 3 weeks at 2 lbs loss per week would've put me at another 6 lbs lost... but 2 weeks reading a total of 3 lbs gain put me 3 lbs up... so 9 lbs off of that put me at my scheduled 6lb loss). The only thing I can figure is that the scale was off because I weighed myself after my workout, after the steam-room, and after I'd drank about 72 fl. oz. of water (which I had yet to get rid of). Coupled with the fact that my body was temporarily holding onto stuff from my diet, because I was depriving it of rebuilding supplies...
It could've been anything. The point is, as discouraged as I was, I kept going, and said, "Just get through this week, and keep doing what you're doing." I also had the favor of the tape-measure, which told me I was still losing SIZE, if not weight. You should definitely keep track of both from week-to-week (not daily). I use the cm side, because it makes changes more pronounced.
And whether the scale tells you what you want or not, take heart that you're a work in progress, and not every week is going to agree with you. There are bumps along the road - the key is to not get hung up on them, but to keep going.
--Janis