So this is an old Mixet shower valve. You can try ordering the parts for a rebuild and changing the cartridge for it, but in my experience the valve body has issues with it. We usually end up replacing them with either a Delta or Moen single handle shower valve.
Source: Plumber for 13 years.
I was in the Navy, we got it drilled in our heads in Boot camp that we had to say Male and Female. Literally we would have to scream "MALE ON DECK" when entering a female's berthing or the opposite when a Female entered a Male berthing.