When sending an email, I am showing 2 of my address's

Outlook version
Outlook 2010 64 bit
Email Account
Using Outlook 2010 with Win 10. I was wondering why people sending return emails where getting the email that I did not send. Today I came across this wierd happening. Somewhere I hit a button that should not have been set. So any help would be nice. It looks like this
John Doe <xxxxx@xxx.com> on behalf of John Doe <yyyyyy@yyy.com>