Also, I find that if I eat certain LC products, or drink aspartame (diet soda), it will knock me out of ketosis, every time.

Since you didn't list a menu of what you're eating and/or drinking, I can't even speculate what the problem may be. There may not even be a problem at all, as a previous poster said, you may just be consuming all the ketones your body is producing and not "spilling" any out into your urine. If this is true, then don't worry about it. I mean, what's the point of carb control, anyway? Is it to shed unwanted bodyfat, or to "turn the pee sticks purple"?