It is probably how estrogen and progesterone levels cycle. I can go up 7 lbs easily and then around ovulation or right after TOM I loose everything and some more within two to four days. It is just water retention and at least in my case it got a lot more pronounced with age. I also exercise and change things up frequently. So, muscle repair will further enhance water retention. I just stick to what I am doing and ignore the ups as best as I can.