Assuming no mistake, I guess you are somehow intolerant to aspartame.
The thing is : for almost every substance, someone will be found intolerant. And I'm not just talking about chemicals, after all, diabetics can't handle regular sugar normally.
Except that intolerances like this may not show up during testing, only when the product is out in the market for millions of people to consume. And of course, a substance that make some people sick, even if it is one in a million, will get bad PR.
As a result, companies will stop using it (a good thing for intolerant people) but they will also replace it with another substance that will probably make other people sick, and the cycle repeats again.
My opinion is that we should stop sweetening everything : no sugar, HFCS, aspartame, sucralose, stevia, etc... Learn to appreciate tastes more complex than the sweetness we are hardwired to love like an addictive drug. It won't completely solve the problem but it would be a great step forward. And we should promote variety too.