God my Oh! is simply the reverse of Oh my God!.
and still means the same.
most of the time when it is used the commenter is trying to be random.
The origin of this word/catchphrase came from an episode of an anime called: Panty & Stocking with Garterbelt.
Just before a character got blown up he said: "Oh my God!"
but when he was resurrected (the scene of him blowing up in reverse) he said "God my Oh!" instead of "ho ym dog".
Comment1: Oh my god. (or OMG)
Comment2: God my Oh!
Comment17: What the f#ck, sweet video man.
Comment19: Fuck the what.