Used to happen to me all the time. I used to have to dress nice for work, and being a big gal, I wore long skirts and dark blouses, and still got called "sir". I moved to the PNW and started wearing jeans and T-shirts, and it no longer happens!? I'm assuming something happened to me (or my voice?) when I got into my mid-30s?
I don't wear makup.
Maybe you need tighter tops?