Hello and hope you are doing well.
Your symptoms of postnasal drip and throat irritation could most probably be due to allergens. These are substances like pollen, dust, animal dander, certain foods, insect venoms and certain medications. Exposure to allergens causes a runny nose with a resultant post nasal drip where secretions from the nose go backward into the throat and irritate causing throat congestion. You will need to consult your primary care physician for proper clinical assessment. In the meantime for relief from your symptoms you could do warm salt gargles and take OTC antihistamines.
Hope this helped and do keep us posted.
This seems to have to do with GERD. Because you are having post nasal drip, it drips down into your stomach and upset your stomach's flora and will create GERD, which is like indegestion or heartburn. I had the same issue and this is what my ENT told me. Don't worry about it. It will go away, always has for me.