My breath smells after I brush my teeth even when I use tooth paste and mouth wash 20 minutes later horrible breath how do I fix this or prevent it?

Causes of Halitosis. The other common causes for bad breath are chronic sinusitis, odor can come from the post nasal discharge. It can also come from your lungs such as after eating food rich in garlic. Systemic diseases can also cause bad breath. You should see an otolaryngologist if problem persists.
Other sources. If your oral health is otherwise good ie., no cavities or gum disease the the source of the odor may be coming from some where else. Often people get bad breath from post-nasal drip or gases coming up from the stomach as in gastric reflux. Get a dental exam first and then go from there.
A few things. Do you have any cavities and do you visit the dentist regularly every 6 months for check ups? Cavities and gum disease can cause bad breath even if you brush and use mouth wash. Also, do you floss your teeth? Consider cleaning your tongue as this is another potential cause of bad breath. I assume you are of 19 years of age. Sometimes the wisdom teeth sites can cause bad breath. Good luck.
Halitosis. You may have vsc's. Volatile sulfur compounds foed fom sulfur comtaining Amino Acids found in protein. Usinf a moith rinse that inactivatea these compounds ia recommended. Oxyfresh is a good one.
Bad Breath. There are many causes of bad breath - most are in the mouth, such as teeth or gum disease. Chronic sinus infections, reflux of stomach acid, and chronic bronchial infections may also be to blame. Most are due to gum or teeth bacteria. Mouth bacterial produce sulfur as a metabolic byproduct. Trying gargling with a lysterine first.