My 18 Year Old Son Has Been Sick Since Monday

My 18 year old son has been sick since Monday fever throwing up thought it was flu. Went to ER last night blood work good X-ray good given iv, said gastritis, and viral. He is white complaining of burning in chest cNt keep food down says it feels like something is blocking his esophagus. Going to pediatrician tom., still has fever, acid and cannot keep anything down including liquids