Boyfriend calling me another girl's name!

Ask him if he's getting into arguments with his sister. When I've been fighting with my sister I tend to call other people by my sisters name, even my girlfriend.
It's the same with my girlfriend, if I've been seeing her for a long period of time, I will start saying her name instead of somebody else's. It's embarrassing some of the time, but it happens to everyone.

You don't live in the Midwest do you?

I doubt it means anything, he was probably thinking about her for some reason, or a slip of the tongue.

Now,... if everytime that you all have sex he starts screaming her name, then I might worry.

Maybe word association? Perhaps you've got a trait or two that he likes (or dislikes) that remind him of his sibling and so those brain neurons are grouped together. It's a little odd, but people are odd sometimes, you know.

People do that.

Haven't you ever called someone the wrong name? I call my dad, "mom" and my mom, "dad" and my friends I get mixed up all the time! lol. I know their names, I just speak to fast.

He sees his sister everyday. He is just used to it.

Now, if he said his sisters name while you were having sex...? wow. that's a different story.