Dull Ache To Burning Pain At Bottom Of Esophagus, Worsened With Sitting, Lying Down. Belching, Diarrhea, Cough. Advice

The bottom of esophagus hurts, almost feeling as if my sternum is bruised. It ranges from a dull ache, to burning. It goes away whenever I drink water, however returns almost immediately after. It feels fine when I am moving around/standing, however sitting and laying down it seems to occur more often. I have been belching more often, and have had diarrhea for the past few days. I have been coughing as well. Sometimes I find I lose my breath, but at this same time its me noticing the pain and become worried/anxious and panicking slightly about what is happening to my chest.