Not making sense

Dieting is becoming confusing for me.  As I mentioned in a previous post, I seemed to gain 2 lbs for no reason - I had been staying within my calorie limit.  Last night we went out and I totally pigged out.  Seriously pigged out - potato chips, green chili dip, candy bars, mexican food, donuts, wine.  Today I weigh myself and weigh a pound less than I did the day before.  Really starting to think my scale is broken...