Child has painful lump in neck, painful swallowing, coughing blood for 18 months. chest xrays clear. gerd + asthma meds not helping. what could it be?

Many possibilities.: 18 months is a long time for a child to be ill without a formal diagnosis. Sometimes blood with coughing is actually from the tonsils or sinus drainage, so look to the head as well as the chest and esophagus. After ENT exam, more thorough pulmonary studies like CT scan or bronchoscopy may be indicated, as well as GI endoscopy to assess esophageal inflammation like EE.