I always seem to have "gained" 3-4 pounds a day or two at the start of my period. I look at it like a motivator to stay on track and then it's like a magical gift a few days later when the scale seems to drop 3-4 overnight. Don't sweat it. Keep at it and you will see results.
"The grass ain't greener, the wine ain't sweeter, either side of the hill" The Grateful Dead