Why do people ignore me?

When I'm alone, I usually don't have this issue. I mean I'm a short person and sometimes people overlook me, but it's especially obvious when I'm out with my husband. People talking to us will focus all their attention on him, ignore me when I talk, etc. I make good eye contact and consider myself fairly assertive. It's so frustrating being ignored that I just don't know what's wrong with me!! Any ideas?