Been having excess mucus after I eat almost anything. Is it an allergy to the food? Had it tonight with sweet potato. Or could it be bc of GERD?

Hard to know. Secretions from the nasal mucosa that increase after a meal is usually due to firing of nerves related to food digestion, but that have side effects in the nose. Its called gustatory rhinitis and is treatable with nasal medication if severe or bothersome. Acid reflux can certainly worsen rhinitis, but usually not immediately unless there is also heartburn/metalic taste. Not food allergy.