Oh yes! Usually 4-5 pounds for me every month. I'm on the Pill to try to regulate my hormones (looooooooong story). Glad I'm not the only one who got incredibly discouraged with WW because of this too
Because the Pill at least gives me SOME predictability (although not this last month) my master tracking sheet for my weigh-ins actually rates each week as "green" (a week totally unaffected by period water gain), "yellow" (might be affected), or--my personal favorite, NOT--the "red" week where progress not only stops but may record in the wrong direction. Knowing that it's water gain is one thing, but there's still the psychological power of the scale, and darn it all, I just can't give up my weigh-ins. BUT....with the stoplight sort of color scheme, I expect very different things from each weigh-in and look forward to my two "green" weeks each cycle :-)
I use the stoplight system to adjust my expectations by week too since I also fight incredible hungry during a red week so at most, my goal those weeks is to maintain if possible and on calorie intake, I usually allow myself to go up to my active metabolic rate if I need to so that I don't end up in a binge mode.