What would cause the throat, tongue and mouth to burn? Tests on heart have been done, heart is fine. Many medicines for GERD they don't help.

Burning Mouth. Syndrome is something dentists are trained to help you with. Since it would seem you have ruled out other systemic problems (heart & GERD) you should talk to your dentist who may be able to identify a medication you take now that causes it or detect a fungal problem which is the most common reason for burning mouth and find solutions.
Dry mouth? If your nose is congested & you breath through your mouth, it can cause dryness of mucus mabrane of the mouth leading to pain & burning, keep your mouth moist with frequent sips of water, use saline nasal spray or gel to clear your nose especially at night. I hope that helps. Good luck .