There are many reasons for halitosis. The commonest of them is the presence of deposits called as calculus on the teeth. You need to undergo a proper clinical examination by a dentist for the evaluation of your situation and delineation of the treatment options available for you. You will be requiring a session of a procedure called as scaling to remove those deposits from the teeth which your toothbrush cannot remove. Chewing gums or mouth fresheners can subside the bad smell for sometime but cannot eliminate it. So they should not be sought after as a remedy to this problem. At the same time you need to maintain your level of hydration because dehydration also is one of the common reasons for halitosis. And don't forget to clean your tongue with your toothbrush every time after you brush your teeth. Use of wooden or plastic or metal tongue cleaner should be avoided because it causes more harm than good. If you have a problem of in digestion, a physician consultation will be required to take care of that problem so that secondary cause of halitosis can be eliminated. Regards.