Hi Princess! The same exact thing happens to me. For weeks, I am very strict about my caloric intake and cardio/weight training yet not drop weight, then I'll go to a party on a weekend and eat double my allotment and not work out for a couple/few days, and lose weight! Here's what I've chalked it up to: sometimes I think the increase in my caloric intake works to kickstart my metabolism. You may have heard this theory elsewhere, and even on this website, but essentially the idea is to work on eating an average amount of calories over the course of a week, but not the same amount each day, so as to keep your metabolism running well and not becoming acclimated to a certain level. For example, one might consume 1200 calories Monday, 1300 Tuesday, 1150 Wednesday, 1500 Thursday, and so on such that a daily average ends up being 1300 or whatever number is appropriate for that person. This is in contrast to eating 1300 calories every single day.
At any rate, you're not alone, and this phenomenon is quite possibly just the result of your body getting kicked into gear by having more fuel kicked into it for a day or so. I do have to share with you that it has been dangerous thinking for me in the past to say,"Hmm, I ate 2 donuts a few days ago and I actually lost weight...the more donuts, the better!"

Just use your head, and you'll do great. Congratulations on your awesome loss thus far!