Why?!?!?

Is someone trying to get into my email account?!?! I don't get it. About a month ago, I noticed that one of my emails showed forwarded. I know I didn't forward it. I checked my sent email....not there. I pushed forward on another email, then closed out without sending...and there was no forward. So then I actually forwarded one, and it was in my sent emails. So.... Someone sent this email somewhere...and deleted it from my email account so I didn't know who it was. Now...this email was personal. It was between me and William and had some inside jokes. I had made a sexual joke about an email he wrote, so he then made a sexual joke about something I wrote. I don't know who would want that email or why. But it bothered me. So I changed my email password. Now...I keep getting notices that my email is being added to some Yahoo ID that isn't mine. It starts with al..... but they don't release the entire ID. SOOOOO.... I am wondering why someone is trying to get my email attached to their Yahoo user ID??? And why they want my emails?!? I don't know if I should change my email address or what. Its driving me nuts!!!!