Excess sticky clear mucous back of throat / nose - continually trying to swallow, after eating anything. not just spicey or hot or dairy, literally any food. mouth and nose very dry also. possible causes?

This is a nonallergic cause of runny nose and increased phlegm production when eating. Histamine-rich foods or foods that prompt your body to produce histamine can create mucus. However, this is typically only an issue for those with a histamine sensitivity or intolerance, which is thought to be the result of enzyme deficiencies in your gut according to April 2021 research in ​Nutrients.

What you described is a common, normal occurrence. Unless you have other symptoms you may ignore this common annoyance. For healthy diet: http://www.choosemyplate.gov/., exercise 30 minutes/day, drink enough water daily so your urine is mostly colorless, have safe sex, no tobacco alcohol weed or street drugs. Get HPV, Flu and Covid vaccines. Wish you good health!