I guess you are using an invisible character. Are you positioning this character somewhere in the scene? As far as I recall the positioning should be enough to place the text over its "head".
(I never do first-person, so I'm not sure)
If positioning an invisible character is not working - you could use a sprite of a character with one semitransparent pixel (donwside is that a cursor could react when hovering in the right place)
Or use display narration text. Then you can place the text wherever you want.