How is it possible to lose weight and clothes fit tight and feels like i've gained?

I recently lost about 5 pounds, well according to 2 scales at least.

Ok, I was heavily working out daily in the beginning of August with running almost everyday. I slacked off almost 2 weeks of no exercise, and now I started up again as of yesterday. Some days I really stick to eating low carb/high fat, and other days I just cheat and eat cookies.

Here's the confusing part, I woke up this morning and weighed myself and was SHOCKED to see that i weigh 124lbs (down from 132lbs.) I couldnt believe this, I thought there must be something wrong with this scale (it is quite old) so I went and got my 5lb dumbells (2 of them) and they weighed accurately. How can it be that i have LOST weight, yet my clothes still fit tight and I have a slight (and I do mean slight) belly?

I'm so confused...........