Help! Does your weight fluctuate as your losing weight

I weigh at the same time every day, wearing the same thing. I can eat below maintenance, everyday for a month, eating mostly whole foods and exercising at least 3 days a week, BUT my weight fluctuate within an 8 pound range. On any given day, my weight will fall anywhere within that wide, wide window. Once it even jumped 8 pounds in less than 24 hours! However, it typically works its way up over 3 or 4 days, and then come down over the course of a week. Sometimes I can pin point an activity or food, or series of foods, that cause the fluctuation, but more than 1/2 the time I can't even hazard a guess. I've lost 120 pounds with this up and down thing. People sometimes ask me how much I've lost, and I always have to think and sort of guesstimate what I think it is, within that range. I tend to assume if I'm eating right and below maintenance, and not dehydrated, whatever the last, lowest weight I got, is the right now. If I'm eating too much, I assume it is several pounds above that lowest weight.