Hello Sumin: This issue concerns the distinction between plain verb use, (feel) and the Present Participle form of the verb (feeling). .

The difference is that one is simple present "I feel" and the other is present continuous "I am feeling". You can use simple present to say things that you (or anybody) normally do (or does). I sing, I dance They speak Latin. You use present continuous for things that you are doing in this very moment. I am dancing (now) I am singing (now) They are speaking Latin (now) I hope this helps.

You should not say "I am feeling happy" You can say "I am happy", "I am tired". It's more simply and usual. You are feeling at this moment For example, I have felt tired couple a weeks, but I am happy now, this feeling has gone from me

They are almost the same. If someone asks you, "how do you feel?" you can say "I feel happy." if they ask you, "how are you feeling?", you can say "I'm feeling happy"