Apparently I have no last name

At least that's what it would seem people think. Any piece of mail Doug and I receive that is addressed to us always says "Mr. Doug LastName and Jamie." And it is not because the senders of said mail do not know my last name. They are all family and close friends who could at the very least find my last name on facebook if they have forgotten it. We received a wedding invitation this week addresses like that, and I can't help but being annoyed. Am I wrong to feel like this is how you would address the invitation to Doug and his (fictional) child? Even having it addressed to Doug and Jamie LastName, though we aren't married yet, would be preferable to me.