Autofill is not working correctly, it adds an extra piece to my email address and I'm beyond frustrated

Hi guys, I'm feeling sick from frustration, and I cant find a solution anywhere else on the internet or other forums. I purchased a macbook pro with retina display running OS X Yosemite. My autofill is driving me up the wall. I have two, very similar email address. one of them is xxxxx.yyyy@gmail.com and the other one is xxxxx.yyyy@yahoo.com (the end part changes from @yahoo to @gmail). Basically, the computer automatically fills xxxx.yyyy@gmail.com on any program on the computer and for any website. It also adds my surname to the end of the email address?? I.E i type in the first part of the email address and it completes it to xxxxx.yyyy@gmail.comavern. Not only is this extremely frustrating, but it wont let me remove it and retry, it keeps autofilling to that address. Not only that, but I use both email address's the same amount, so to try and use my yahoo account is almost impossible, as it always autofills to the incorrect gmail address. I thought I would be able to write the proper yahoo address on notepad and copy paste, but the thing autofills on there as well!!! Im feeling really hopeless, and I went onto safari and unchecked ALL autofill settings, as well as my contact card in the hopes it would stop autofilling, but it was unsuccessful. PLEASE can someone help me!!

Thanks