There is a new feature in Google Mail whereby you can see if more than one person is accessing your account. From there you can see if someone is accessing it without your knowledge, you can easily trace who last logged in to your mail account.
Find out who hacked my Gmail account?
Firstly, log into your Gmail account and scroll down to the bottom of the page. There is a section called “Last account activity”. It will show you information like who logged in and the time duration.