Tongue scraping (scrapers available from places like Boots and Superdrug as well as pharmacies) and changing your diet may help. Are you starving yourself? Or on a strange new-fangled diet? Not eating gives you bad breath. But as PaulB says, at the end of the day, there's no substitute for going to the Dentist.
I get bad breath if I don't drink my usual amount of water, which is 4 litres a day. In fact I notice the breath before I even realise I'm getting thirsty. And I always carry sugar free gum. There's no point in gum with sugar as this feeds the bacteria in your mouth and pretty soon you're back to dragon breath!