First, take a wet face cloth and wipe down your tongue and roof of mouth whenever you brush your teeth. Works better than using a brush on the tongue.
Second, you might have tonsil stones (tonsoliths) which are common. I posted a few times about how to get rid of them so you can search. They smell like... something a dog would faint over, and one little stone lodged in your tonsils will make your whole mouth smell foul.