hi, my throught at the back of my nose feels sore. it's alright during the day but in the evening it starts feeling sore and at night it gets really dry. the mucus goes from clear during the day to yellow in the first hours of the morning, with a slight odour, not a bad one necessarely but one that is detectable. when it starts giving me discomfort, my whole nose feels dry as I breath in... what could it be?