First of all congratulations on your 21 pound wt loss...21 pounds in 2 weeks wow amazing...is that safe though...
Now for your question; yes I find it hard to loose during that week I read somewhere that due to harmonal changes during your periods your body does not tend to loose any wt...but you still managed to loose a pound..so thats not bad ..i know it is nothing compared to the 10.5 pounds u lost in a week...but thats the way our womens bodies work....