Several internal medical conditions can cause your breath to go downhill fast. They include diabetes, liver disease, respiratory tract infections, and chronic bronchitis. You'll want to see your doctor to rule out things like acid reflux, postnasal drip, and other causes of chronic dry mouth (xerostomia).
Bad breath can also be caused by a buildup of bacteria in your mouth that causes inflammation and gives off noxious odors or gases that smell like sulfur. Studies show that about 80% of bad breath comes from an oral source. For instance, cavities, gum disease, plaque on the tongue that have trapped food particles, cracked fillings, and poorly maintained dentures can all cause bad breath.
Your dentist can help you determine whether any of these conditions are contributing to your bad breath and help you find treatment solutions.