How is your sugar intake?. Anything with sugar in it, even a mint, can make your teeth icky and hard to clean. Same goes for starchy foods. If that isn't the problem you may want to try a different toothpaste and /or toothbrush.
Try this home made herbal mouthwash. Take a few sprigs of parsley and 2-3 whole cloves (you can probably find both in the local grocery store). Put 2 cups of water in a pan. Add the parsley (coarsely chopped) and the cloves. Boil and then let it cool. Stir frequently while the mixture is cooling. Your homemade herbal mouthwash is ready!