You've only been on LC three weeks, so by definition you are not stalled. A stall is four to six weeks with no weight loss or loss in inches with no changes in your diet or exercise routine. Nearly everyone stops losing weight after the induction period, because most of the induction loss is water. After induction, you will usually lose more fat and replenish the lost water, hence the weight equilibrium. This is normal and natural, so don't stress out about it.

So don't be so quick to assume that aspartame is a "staller" for you -- my guess is that it doesn't have anything at all to do with your weight loss this week. You just don't have enough data at this point to draw that conclusion -- give it a little time. Of course, heavy consumption of aspartame is not generally a wonderful idea no matter which diet you're on, and homemade LC treats are almost always a better idea than the prepackaged versions.

As for 8 lbs. in three weeks, that's a reasonably good rate of loss. The biggest myth about Atkins is that it's a fast weight loss diet -- it's not, except during the induction period (which, again, is mainly water). After the initial loss, most people continue at a rate of one to three pounds a week. It's not necessarily much faster than WW (when it works) -- but it's more fun, and it often works for people who are insulin-sensitive and have slowed or stopped on LF diets. It's also very important to measure yourself, as it's very common to lose inches while the scale remains the same.

Don't stress out! Give it a month or two of following the guidelines in the book before you decide to start tinkering or fretting. Relax and enjoy what you're eating and how you're feeling!