Viral Gastroenteritis: This is the most likely diagnosis given the symptoms of vomiting and abdominal pain without fever, and a negative Covid-19 test. The absence of fever and the negative Covid-19 test reduce the likelihood of other infectious causes, making viral gastroenteritis a plausible explanation.

Constipation: Constipation can cause abdominal pain and vomiting, especially if the constipation is severe. It's a common issue in children and can be easily overlooked.
Functional Dyspepsia: This condition is characterized by recurring abdominal pain and vomiting without an identifiable cause. It's a common diagnosis in children with chronic abdominal complaints.
Food Poisoning: Although the child has been symptomatic for 5 days, food poisoning could still be a consideration, especially if the child has been consuming the same contaminated food over several days.

Appendicitis: Although the child does not have a fever, appendicitis can present with vomiting and abdominal pain. It's crucial to consider this diagnosis to avoid missing a potentially life-threatening condition.
Intussusception: This is a condition where a part of the intestine slides into another, causing bowel obstruction. It's a medical emergency that requires prompt attention.
Inflammatory Bowel Disease (IBD): Conditions like Crohn's disease and ulcerative colitis can cause chronic abdominal pain, vomiting, and other symptoms. Early diagnosis and treatment are essential to manage the disease.

Gastric Volvulus: A rare condition where the stomach twists abnormally, causing severe abdominal pain and vomiting.
Malrotation with Midgut Volvulus: A congenital condition that can cause intestinal obstruction and ischemia, presenting with abdominal pain and vomiting.
Hirschsprung's Disease: A congenital condition affecting the colon, leading to severe constipation, abdominal pain, and vomiting. Although typically diagnosed in infancy, some cases may be diagnosed later in childhood.