Only One Space??

Alright, call me crazy, but I did not know that you are only supposed to put one space after the end of a sentence. I was always told in school that it is two, and no one has corrected me. This is driving me nuts, I had to take a typing test for a job interview today and had to start over a couple of times because my thumb is trained to do two spaces, not just one. When did this change, and where the hell was I? I mean, I type about 70-80 wpm, and trying to retrain my fingers is going to be impossible. I have to keep fixing this post as I write it! All I can keep thinking is of the word documents I've got piled up on my laptop that are full of these double spaces. Tell me I'm not the only one that was oblivious to this change...