bad bad breath DENTISTS?!

Two things come to mind when I hear bad breath, NUG and geographic tongue. You probably don't have either of them.

Type geographic tongue into google images. Now look at your tongue. Does it resemble any of those pictures? Well, if it does, you might have geographic tongue. There's no treatment for it, but to prevent the bad breath associated with it, you should brush your tongue twice a day.

NUG -- I bet I can safely assume you don't have this. It's pretty rare for people to get this. It's also called trench mouth because soldiers fighting during WW1 would often develop NUG. It's a form of gingivitis characterized by bad breath (really really bad breath). You wouldn't get it though unless you were malnourished, sick, and/or not caring for your teeth.

Bottom line you probably DON'T have NUG or geographic tongue. Brush your teeth thoroughly twice a day and remember to get your tongue too. Floss once a day. A lot of people think they know how to floss, but they actually don't. Look for a youtube video on how to floss properly.

not a dentist, but someday I will be

Well.. the first thing would be you do not brush properly and might have some calculus deposits around your teeth which make your breath smell bad.
Another probable cause could be you not cleaning your tongue. Buy a tongue scrapper and clean the deposits starting from posterior part of your tongue and to the tip in a go.. I am sure you know how to use it.

It takes sometime for halitosis to go away but you will start feeling the difference right away if you start brushin twice. Once after the last meal in the night and the next after breakfast. Before breakfast you wanna use a mouthrinse in some luke warm water. Rinse your mouth with plain water after each meal.

Also go for a dental check up .

There could be various reasons for halitosis but for now lets stick to the basics.

I am a dentist

firstly how is your oral hygiene do you brush twice daily?basic reason is improper brushing technique
see fones technique(google it).also use a tongue cleaner to remove any kind of debris from your tongue.
secondly do you have a prosthesis(crown,bridge,partial denture) are you maintaining proper hygiene in these areas ?
begin a habit of using mouthwash(listerine) after brushing do not eat ,drink anything for 30Min'ss after using mouthwash
did you consume any food having onion/garlic in it ? brush ,mouth rinse
visit your dentist every 6 months for a check up and scaling