I’m 22 and I had same symptoms and it turned out to be GERD, basically extreme acid reflux. I remember during the vaping illness scare I freaked the fuck out and became ultra healthy and took up running again and when I finally decided I had to go to the doctor due to a cough which wouldn’t go away she basically asked some simple questions and mentioned the bad breath (my ex used to always say I had bad breath esp in the mornings lol) and I was prescribed some anti-biotic stomach medication (think it started with a p) and kept a bottle of peptcid on me just in case. It’s definitely manageable but you will probably have to quit drinking coffee and tomatoes anything acidic except basically meat and salad for awhile. Take care!