Bad smell could be not only due to problems originating from your mouth, but also because of underlying problems in your respiratory system or digestive system. Visit a dentist to know if the problem is solely originating from mouth. If this is the case, it can be treated by scaling and use of mouthrinses. But please remember, using only a mouthwash without knowing the actual reason for bad smell might give only temporary masking effect..you will only feel fresh as long as the power of the mouthwash is active.
Next Steps
If the problem continues even after thorough cleaning of your teeth, gums and tongue, then your dentist might refer you to ENT doctor (for throat infections, sinusitis, nose block, tonsilitis, etc) or a gastroenterologist (for digestion problems, acidity, gastritis, etc).
Health Tips
Don't just concentrate on your teeth and gums while brushing, give equal importance to clean your tongue...because as many as 90% of bacteria and other microorganisms of entire mouth hide within the irregular surface of your tongue.