That might be halitosis my friend. CONGRATS!!!
Mouth uncomfortable because of hot, smelly breath. Floss, brush daily still there. Dentists doesn't know what's causing it?
If it's not oral .. Then it's probably digestive. See your doctor.
I would switch from Listerine for a week to a 50/50 mixture of water and hydrogen peroxide. I would also suggest the same as Bikergirl and make an appointment with your physician. Having had digestive issues, I can tell you that they can make for some nasty smelling and tasting breath.
You may have what's called a tonsil stone. In simple terms, it's a build up of bacteria, dead cells in the areas of the tonsils, some of which may be hidden from you. These cause foul smelling breath, if you can see one, you can try and brush it free with a toothbrush, gargle with warm salt water to help this.
Go to your doctor he/she can test you for other causes as bad breath can be a symptom of other conditions. Stomach problems and acid reflux can cause problems with bad breath. My partner suffers with hiatus hernia, and from time to time his breath smells acidic. He takes omeprazole to ease the problem. Make sure you brush your tongue.
Johnny Bravo, here is something else for you to consider...
There is much stress in your life right now; and I am not sure this is fully documented, but imo stress can throw your body systems off balance.
And a lot of that imbalance begins with the digestive system.
So, yes indeed see your physician for a full check-up, telling him/her about your breath. If nothing shows up, then I don't know how funds are for you right now but can you see a naturopath? Or Traditional Chinese Medicine?
I bring this up because alternative medicine is trained to detect and treat metabolic imbalances while they are still subclinical, that is you have the symptoms but the standard medical tests will not detect any problem.
If the physical checkup is okay and you cannot see a naturopath, then if you can, just do your own reading, meanwhile get the best nutrition possible. Can you eat fresh (or frozen) fruit in the morning, for example? Fruit helps the body detoxify...* * *
Also, exercise, plenty of water...they help the body detoxify; see if you can work in a regular program.
Several internal medical conditions also can cause your breath to go downhill fast.
http://www.webmd.com/oral-health/guide/change-your-breath-from-bad-to-good#1