Get rid of a 'gay' lisp, (see details)?

So I am 16, almost 17 and I appear to have a "gay" lisp. The voice sterotypically attributed with gay men. Well, I am not gay, so this is a problem. When girls talk to me they just ume that I am so I become a 'friend' instead of more. And on the phone people think I am a girl. Does anyone know of any vocal exercise or anything I can do?