Best thing I've learned to monitor progress is to hold your scale firmly in both hands...then with a smooth single motion through the wrists...toss it through the nearest (open) window.
The scale has been the single most important invention of frustration and disappointment ever.
Look at photos from 6 months ago. Compare them to photos from now. Pretty sure you will see a significant difference that trumps any number on the scale. Have your energy level increased? Has your self confidence increased when you're Not looking at the scale? Has you strength increased and clothes began to fit loser? These are valid markers of progress and "weight loss". Fat loss is more like it.
I've gotten on the scale at 6 am and seen 181, then for shitsandgiggles stepped on again later in the evening and it's said 178. The next day it would say 177. Later that day 179. Weight fluctuates, especially in women.
But if you're dead set on wanting to know your numbers; check first thing in the morning once a week. Recalculate your caloric needs for that week using the Mifflin - St Jeor equation (10 * weight(kg) + 6.25 * height(cm) - 5 * age(y) - 161 =BMR) and drop between 500 - 1000 calories from your BMR. (10 - 20% decrease )
Anything more than a 20% deficit will be essentially starving yourself. Don't do that.
Heh...do people bail out if they are faced with reality?!
I'm also using myfitnesspal to monitor caloric intake, so I can tweak the settings a bit from your advice about weekly calculations. I've just been keeping the calories at the same level (reduced from normal), but I hadn't thought of changing it often as you've mentioned. So, that was also helpful. :)