I don't know where it came from. I use it as an all purpose word that encompasses many different emotions and feelings.
Where did I come from? I don't remember ever starting to say it... I just remember always saying it.
That sounds like a fancy word ;D
But I don't say it. I do say Buuuuuh, hurrr, durrr, derp, Blarg.... and many other random noises and made up words.