From what I've read, aspartame isn't always a problem. If you consume aspartame and keep losing weight, great, no problem! You can tell if it's a problem for you if you stop losing weight, get rid of the aspartame, and resume losing weight.

Be careful with those sugar alcohols, though, they're laxatives. I found that out the hard way...you should be fine if you don't consume too many, though!