Inflammatory Bowel Disease (IBD): This includes conditions like Ulcerative Colitis (UC) and Crohn's Disease (CD). The presentation of bloody diarrhea and abdominal pain without fever is consistent with IBD, especially UC, which often presents with bloody stools and can start at any age, including adolescence.

Infectious Colitis: Bacterial infections such as Campylobacter, Salmonella, or Shigella can cause bloody diarrhea. The absence of fever does not rule out these infections, as some patients may not present with fever.
Food Poisoning: Certain types of food poisoning can cause bloody diarrhea, though this is less common.
Intestinal Infection with Parasites: Though less common, parasites like Entamoeba histolytica can cause bloody diarrhea.

Intussusception: A condition where a part of the intestine slides into an adjacent part, which can cause bowel obstruction and ischemia. It's a surgical emergency and can present with bloody stools and abdominal pain.
Meckel's Diverticulum: A congenital anomaly of the small intestine that can cause bleeding and may present with painless or painful bloody diarrhea.
Ischemic Colitis: Reduced blood flow to the colon can cause bloody diarrhea and abdominal pain. This condition requires prompt diagnosis and treatment to prevent complications.

Hemolytic Uremic Syndrome (HUS): Typically follows a diarrheal illness caused by E. coli O157:H7, leading to kidney failure and hemolytic anemia. It's rare but serious and can present with bloody diarrhea.
Colonic Polyps or Cancer: Though extremely rare in adolescents, any new onset of bloody diarrhea warrants consideration of these conditions, especially if there's a family history.
Vasculitis: Conditions like Henoch-Schönlein purpura can cause abdominal pain and bloody diarrhea, though they are rare and usually accompanied by other symptoms like rash and joint pain.

Management will depend on the suspected diagnosis but generally includes:

Stool tests for infectious causes
Endoscopy and biopsy for IBD and other structural abnormalities
Imaging studies (e.g., ultrasound, CT scan) for conditions like intussusception or ischemic colitis
Supportive care, including hydration and possibly blood transfusions for significant blood loss
Antibiotics for bacterial infections
Specific treatments based on the diagnosis, such as aminosalicylates or biologics for IBD, and surgery for conditions like intussusception or Meckel's diverticulum.