What can I do for constant halitosis?

Check with dentist. Constant halitosis (bad breath) can be caused by a number of things: tooth decay gum disease poor oral hygiene (do you brush properly, do you floss, do you brush or clean your tongue). It can also be caused by your diet. It can also be a sign of a systemic disease. Check with your dentist.
Find the cause. There are many causes of bad breath, both of dental and medical origin. Find the cause(s) and treat them and then maintain good oral hygiene. By far the most common cause is poor oral hygiene. See the following website for more information: http://www.Smilesapartcosmeticdentist.Com/fresh-breath-control.Htm.
Flossing & Brushing. If the flossing doesn't eliminate it; you might want to consul an upper g i specialist.
FULL MOUTH DETOX . Bad breath is caused by odor producing bacteria in your mouth. It is almost impossible to remove those billions of bacteria from your mouth by simply brushing, flossing, or mouthwash. Yes, after you brush-floss-rinse-chew gum-rinse again-floss-brush again... Then for few minutes you will not have bad breath... The only way to get rid of it- is to do full mouth detox procedure, we exclusively do it.