This happened to me with an anti-biotic when I took it without food and went to bed not long after. Some medications can reflux on you and can actually burn the bottom of your oesophagus. It feels exactly like you described. Mine lasted for about 4 days. If it is really bad, it may be ulcerated from the chemical burn. Either go back to your dr for advice or contact the company who makes the medicine for some advice. Hope this helps.