This is unfortunately a problem with my mod, if you're using it, it assigns a random portrait to every slave and there's no differentiation to one created for the player vs. any other. So if you have my random portraits mod enabled and start a new game, you'll be getting a random portrait for your main character.
I've been meaning to see if I can implement a work-around, something that resets it back to the default figures during character creation or something, but haven't yet. Dunno if Lazerus's method works or not, but if it doesn't, you can edit your save, first search for "player": then search for first "imagefull": after that, and change it's value to null, "imagefull":null