I always feel the need to eat something to take that nasty after taste out of my mouth. I’m not a breakfast eater, so I don’t eat much or anything in the mornings, not sure if that plays a part in this as well.
Have you checked your saliva PH level in the morning ? You can get a roll of PH paper and just spit it on in the morning when you wake up. I was having terrible morning breath which was not usual for me.. I checked and the PH was 5.5 . I'm taking Coral Calcium liquid now and "Miracle PHour" , and my morning PH is up to about 6.5 and the bad taste and breath has improved.. but I have a small cavity or maybe two that I need to fix. If you have a hidden cavity that your dentist is not detecting, it would very surely cause bad taste and bad breath. In my experience it is possible for a dentist to miss a cavity, I'd try to go to another for a free exam if possible. It's also possible dentist will tell you have a cavity when you don't though, this has happened to me many years ago, and I know others it happened to as well, so it's very though!
I believe my diet caused low PH saliva which then ate away at my teeth and caused the cavities I've had. Bacteria make acid that causes cavities. Saliva can neutralize that acid. Also I believe neutral PH saliva will not allow bacteria to proliferate like acidic saliva would.
Give the PH paper a try if you can, I'm curious what you will find.