I remember always getting a scratchy throat which turned into post nasal drip, and a sore throat after drinking 2 or more diet sodas. My family always buys diet soda because regular soda is way too sweet that it's sickening sweet.
For years I drank diet soda with my pretzels or chips , or meals. For years I suffered throat and sinus issues.
Cutting out all diet sodas and aspartame, I no longer experience the familiar scratchy throat I always did.
Rule of thumb is, to pay attention to how your body reacts to something because if you get even a minor bad reaction, it's a sign that it's not good for the body.