My Hungarian friend tells me that hátul cannot be translated as "behind." "Are you often in the back" is perfect, but the Hungarian word for behind is mögött.
It would be a wrong sentence. In this case 'vagy' is a personal pronoun, like 'are' in English. But you're right, 'vagy' also means 'or', but the sentence is wrong.
Without the question mark, could this be a statement? ("Gyakran vagy hátul" = "You are often behind.")?