Strange Issue with MacBook Air keyboard

An issue cropped up with my MacBook air when it comes to using quotation marks. I work as an editor, so this is significant.

In the past, I hit SHIFT + " to add a quotation mark at the beginning or the end of a quote.

Now, unless I hit the space bar after hitting SHIFT + " the quotation mark disappears and instead an umlaut is added to the first letter, like this: Ä.

Also, I have to hit the space bar after adding the closing quotation mark or else it adds two quotation marks, like this: "example""

I'm sure this has something to do with my keyboard settings, but I can't figure out what it is. Any help would be appreciated.