The best please to start is to immediately change your password. When that is done verify that all security questions & answers that are associated with the account are only your questions & answers. Also, check all mail forwarding and mail filter rules to make sure that a 3rd party had not added themselves to receive a copy of all your new emails. This is a tactic used by some spammers after your account has been compromised to allow them a way to receive password reset emails so they can get back into your account again after notice their activity and change your password.