Every body is different. Many women gain weight the week prior or week of their period due to "bloating", though I don't typically experience this issue (I think because of all the water I drink), but you do technically burn a few extra calories during your period because of the extra work your body is doing.
Keep in mind also that your body weight is constantly fluctuating. You can fluctuate quite a lot just in a 24 hour period (for instance I was 125 this morning and after lunch I was 130), so you need to choose a specific time of day and specific circumstances for your weekly weigh-in. For instance, my official weigh-in is every Saturday morning right after I get up and use the bathroom, and before I eat or drink anything. I weigh in with those specific circumstances every week, which helps me to keep a more honest view of weight changes.
Also, just I guess for my own peace of mind in case anyone is concerned, I don't actually weigh in multiple times a day. I happened to get on the scale this afternoon to weigh in my 7 month old mix-breed puppy to see where she is (FYI, she is up 4 pounds since a month ago! Yay!), but I do tend to get on the scale most mornings just to check in, though I don't record anything but my Saturday weight.
Edited by: RAINBOWCHARMER at: 1/13/2012 (21:35)