it comes from the Yiddish "oh vez mear". and in response to the 'woe-is-me'ing post, you're incorrect. woe is me is a commonly used phrase and although not grammatically sound, it is in the parlance of our times. No one would say "woe is i". sorry.
you are sitting with your friends and have a self-realization that "these are my friends, wow!". you then would exclaim, with your hands cursing the sky "oh vez mear!" or "woe-is-me"