Gluey Mucus, Pimples on Oropharynx, Back of Hand

Since returning from a disastrous visit to Mexico eleven months ago, I have lived with a spit cup.  White to light yellow foamy, gluey, sticky, thick mucus issues from the back (and sometimes sides) of my mouth 24/7.  A General Practitioner said it was fungus and prescribed Fluconazole, which did nothing to stop the mucus but made my lips dry up and peel off several times a day.  An ENT doctor prescribed Nystatin oral, which caused severe rashes everywhere and an allergic reaction that had me bedridden. Sputum tests were negative for candida.  An internal medicine doctor said I was "toxic," prescribed more Fluconazole, and said to take probiotics.  I've tried vitamins, minerals, colloidal silver, a wide variety of herbs, the Yeast Connection diet, and everything else I could find.  No one seems to be able to figure out what it is: Does this sound like something caused by a virus, fungus, bacteria, parasite, or something else?  I'd like to at least narrow it down and find out what type of doctor to contact.