A little bit of a stolen identity crisis...Need some suggestions?

I recently received an text message from a friend. The text mentioned an e-mail that I had sent her the day before. I had no recollection of sending her an e-mail, so I asked what she was talking about. I come to find that someone had been sending her e-mail, pretending to be me. They had an e-mail address that was very similar to mine, just off by a number, and the name was registered as mine.

She forwarded me the e-mails that “I” sent to her, and this person knew everything about my life. The things he/she were saying were pretty dead on. It was very shocking.

Needless to say, I don’t know who it is, or what I can do about it. I don’t want them e-mailing other people who may think that it’s me.

The girl who got the e-mail, her e-mail is on facebook, so that could have easily been how this person got her e-mail address. But is there anything I can do to stop this? I’m a little worried. Has anyone been in this situation before? I need some help.