I suppose "oh, brother" has the same meaning as sighing. Then, can I say "oh, sister" as well?
Native speaker’s answer
Rebecca
"Oh, brother" is an informal exclamation used to express disappointment or frustration. "Oh, sister" is not used at all, but expressions like "oh, boy" and "oh, man" are! Ex: Oh, brother. Here we go again. Ex: Oh, boy. I accidentally messed it up again.