Visit a gastroenterologist regarding acid reflux of your friend. In case if the symptoms are persistent with the use of over-the-counter medication, then visit a specialist. The loss of weight without any reason is also an alarm symptom which needs to be looked at urgently. 

As soon as you can, go to a gastroenterologist. The symptom of hematemesis – vomiting blood is a serious sign that must not be overlooked. It may refer to various diseases, including gastric ulcers, inflammation of the stomach lining or even cancer. Only an expert can identify the underlying condition.

The location of the pain in the lower right of your stomach, especially when walking, may be a sign of appendicitis. The swelling of the appendix is called appendicitis. The primary clues may also be loss of appetite, nausea, and fever. A doctor must be sought immediately for a full checkup and proper therapy as appendicitis might be dangerous and can involve surgery as a remedy.

From what you have described, your son may be having a gastrointestinal infection based on the recurrent gastric pain of fever and vomiting. Your son should have a comprehensive evaluation and treatment by an experienced gastroenterologist. The specialist may recommend further testing like endoscopy or imaging studies to determine the root of the problem. It is advisable to seek medical attention early in order to avoid any complications.