Cannot use sudo after changing my user password. Cannot access root in any other manner either.

I am running Mint 18.1 on a Toshiba Satellite P75-A and access grub bootloader via ESC at boot. My username is no longer a member of sudo group though it is a member of adm. I am the only user of this computer, and my network is a home network with ethernet and wifi and, typically, only one other user.