still can be thought of as saying an activity is continuing to happen. I am still here . means you are continuing to remain in your current location. I'm still hungry means you continue to be hungry. "yet" is often used negatively, as in :"I'm not home yet" meaning I havn't reached my house. "The treaty has not yet been implimented." meaning the stipulations of treaty are not in effect now, but they will be in the future.

The distinction is not about being positive or negative - it's about whether your statement relates to the past or the future. 'Still' refers to a situation continuing from the past, while (not) 'yet' looks forward to an anticipated situation in the future. 'I'm still not hungry' means that I wasn't hungry earlier and this is still the case now. 'I'm not hungry yet' means that I'm not hungry now but I expect to be hungry later. And no, I'm afraid you can't use 'yet' after the (grammatically) positive statement 'I'm confused'. You have to say 'I'm still confused', or reword the idea to say something like 'I haven't solved this problem yet'. This would imply that you expect to solve the problem eventually, whereas 'I still haven't solved the problem' doesn't necessarily imply that that you expect to do so. NB Don't confuse this use of 'yet' - referring to time - with the separate use of the word in the sense of 'but'. James's second sentence is an example of this unrelated usage.

"I am still confused about it" "I hear what he is saying, yet I am confused about it"

You know the beauty of a natural language is that there are so many different ways to express yourself. Both "I'm still not hungry' AND 'I'm not hungry yet' are perfectly good. It doesn't have to be one or the other, or even one's better than the other. "I'm confused about it yet." on the other hand sounds like a bad sentence. You might be overthinking "yet" when you say "negative connotation". You can simply think of it as "not as of now", and sometimes like "but" depending on context. It reminds of these beautiful closing lines in a Simon and Garfunkel song that I liked when I was learning English long time ago. It has "yet" in it used in a more sophisticated way, as well as many other phrases useful for new English learners to know. ( "Wednesday Morning 3AM" - Simon and Garfunkel, 1964 ) .... My life seems unreal, my crime an illusion, a scene badly written in which I must play. Yet I know as I gaze at my young love beside me, the morning is just a few hours away.

Or another one: " I think I understand, but if he keeps on showing Powerpoint slides, I may yet become confused about it."