If the email is new, there is no doubt that your PC is infected with malware that gives access to hacker.
You might have an installed bitcoin related software, or a coin mining software with a silent virus just waiting for a chance.
You must reformat your PC and reset all your cryto related account passwords.
Yes, Your thought is right . I 'm used to be like this and I lost some bitcoins . You must clear old system or format you HDD and re-setup new system.
I'm sure you will not see this issue anymore.