It seams that some one is reading my e-mails. Help?

Its probably someone who knows your e-mail and is close, there is nothing that you can do because they can even get your password seems like, I've been trying to get my account deactivated but my sister (I just know its her but lack of proof) keeps going into it. The problem is when you ask for a new password they either show it on your screen when you answer the correct question (thats how they always get your new password) or through another e-mail. Its pretty much a waiting game until they get board.